PLANT BREEDING AND THE NUTRITIVE VALUE OF CROP RESIDUES PROCEEDINGS OF A WORKSHOP HELD AT ILCA, ADDIS ABABA, ETHIOPIA 7-10 DECEMBER 1987 JUNE 1988 INTERNATIONAL LIVESTOCK CENTRE FOR AFRICA P.O. BOX 5689, ADDIS ABABA, ETHIOPIA Cover: Zebu oxen eating barley straw in the Ethiopian highlands. ISBN 92-9053-094-4 PLANT BREEDING AND THE NUTRITIVE VALUE OF CROP RESIDUES PROCEEDINGS OF A WORKSHOP HELD AT ILCA, ADDIS ABABA, ETHIOPIA 7-10 DECEMBER 1987 Edited by Jess D. Reed Brian S. Capper PaulJ.H. Neate JUNE 1988 INTERNATIONAL LIVESTOCK CFMTRP pop acdi^a P.O. BOX 5689, ADDIS / This One AWTY-QW3-SGWF Correct citation: Reed J D, Capper B S and Neate P J H (Eds). 1988. Plant breeding and Che nutritive value of crop residues . Proceedings of a workshop held at ILCA, Addis Ababa, Ethiopia, 7-10 December 1987. ILCA, Addis Ababa. ABSTRACT This document contains 12 papers on topics related to the use of crop residues as livestock feed in smallholder crop/livestock farming systems, and the role of plant breeding in maintaining or improving their nutritive value. Workshop ses sions covered the role of crop residues as feed resources in smallholder crop/livestock farming systems (3 papers) ; factors limiting the nutritive value of crop residues (3 papers); the effect of genotype and environment on the nutritive value of crop residues (4 papers) ; and perspectives and implications for crop improvement programmes. A fifth section presents reports of working groups on aspects relating to the main workshop sessions, and makes specific recommendations on areas need ing further research and modes for collaboration between crop and livestock research programmes. KEY WORDS /Crop residues//Animal nutrition//Animal feeding/ /Plant breeding//Smallscale farming//Mixed farming//Nutritive value//Genotype//Environment/ /Research/ in RESUME Le présent document contient 12 communications présentées lors d'un atelier consacré à l'utilisa tion des résidus de récolte comme aliments du bétail dans les systèmes de production mixte, et sur les possibilités d'amélioration de la valeur nutritive de ces résidus par la sélection. Les sessions de cet atelier ont porté sur le rôle des résidus de récolte en tant que ressource fourragère dans les systèmes mixtes (3 communications); sur les facteurs limitant leur valeur nutritive (3 communications); sur l'influence du génotype et du milieu sur cette valeur nutritive (h communications); et sur l'in tégration des critères retenus aux programmes d'amélioration des cultures. Les rapports élaborés par les différents groupes de travail sont présentés dans la cinquième partie de ce document, ainsi que des recommandations sur les axes de recherche prio ritaires et sur les modalités de collaboration entre agronomes et zootechniciens. MOTS CLES /Résidus de récolte//Nutrition animale//Alimentation du bétail//Sélection végétale//Petite exploitation/ /Exploitation mixte//Valeur nutritive//Génotype/ /Environnement//Recherche iv PREFACE The objectives of this workshop were to bring together scientists involved in research on crop improvement, ruminant nutrition, feed chemistry and animal production to: o discuss and assess the effects of current trends in plant breeding on the nutritive value of crop residues; o consider the economic benefits of high- yielding varieties (both grain and residue) to smallholder crop/livestock farming systems; and o identify parameters that need to be monitored in order to maintain high nutritive value of crop residues. The workshop was organised into five sessions, and these form the major divisions of the proceedings. Session 1 set the stage for our deliberations by stressing the importance of crop residues as feed resources in smallholder crop/ livestock farming systems. Session 2 highlighted the problems of using crop residues as feeds by combining presentations on basic problems of feed chemistry and ruminant nutrition. These two sessions, presented during the first day of the workshop, provided the background material for discussions during the next three sessions. Session 3 presented four case studies on the effects of genotype and environment on the nutri tive value of crop residues. Sessions 2 and 3 were presented by feed chemists and ruminant nutritionists. The workshop organisers sincerely appreciated the patience and enthusiasm shown by the scientists associated with crop improvement programmes during these sessions and the construc tive dialogue that developed between scientists from disciplines which, for the most part, are separated by institutional boundaries. Session 4 was intended to present the perspectives and implications for crop improvement programmes primarily from the viewpoint of the plant breeder. However, one problem encountered was to find plant breeders who have participated in this type of research, and only one paper was presented by a plant breeder. Session 5, the concluding session, was also designed to obtain the perspectives of crop scientists, through discussion with scientists from other disciplines, on future prospects for plant breeding to maintain or improve the nutri tive value of crop residues. These discussions led to the recommendations made in the final section of the proceedings. The workshop organis ers wish to express their gratitude to all the participants for their active and constructive involvement in this session. Finally, the organisers wish to thank ILCA and all the other institutions that provided funding for the participants. Each CGIAR centre funded its scientists. The Technical Centre for Agricultural and Rural Co-operation, ACP-EEC Lome Convention, provided funds for the participation of several scientists from national programmes. Participants were also funded by the Overseas Development and Natural Resources Institute and the Institute of Grassland and Animal Production, UK. vi We hope that the proceedings will be useful to researchers interested in crop/livestock interactions and the importance of crop residues as feed resources in smallholder farming systems. Jess Reed Brian Capper Paul Neate April 1988 vii CONTENTS PREFACE SESSION 1: THE ROLE OF CROP RESIDUES AS FEED RESOURCES IN SMALLHOLDER CROP/LIVESTOCK FARMING SYSTEMS Importance of crop residues for feeding livestock in smallholder farming systems R.E. McDowell 3 The availability of crop residues in developing countries in relation to livestock populations Vappu Kossila 29 The importance of crop residues as feed resources in West Asia and North Africa Thomas L. Nordblom 41 General discussion 65 SESSION 2: FACTORS LIMITING THE NUTRITIVE VALUE OF CROP RESIDUES Effect of environment and quality of fibre on the nutritive value of crop residues P.J. Van Soest 71 Phenolics in fibrous crop residues and plants and their effects on the digestion and utilisa tion of carbohydrates and proteins in ruminants I. Mueller-Harvey , A.B. McAllan, M.K. Theodorou and D.E. Beever 97 Practical problems of feeding crop residues E. Owen and A.A.O. Aboud 133 ix General discussion 157 SESSION 3: THE EFFECT OF GENOTYPE AND ENVIRONMENT ON THE NUTRITIVE VALUE OF CROP RESIDUES Consistency of differences in nutritive value of straw from different varieties in different seasons E.R. flrskov 163 Genetic variation in the feeding value of barley and wheat straw B.S. Capper, E.F. Thomson and F. Herbert 177 Sources of variation in the nutritive value of wheat and rice straws G.R. Pearce, J. A. Lee, R.J. Simpson and P.T. Doyle 195 Factors affecting the nutritive value of sorghum and millet crop residues Jess D. Reed, Yilma Kebede and Les K. Fussell 233 General discussion 253 SESSION 4: PERSPECTIVES AND IMPLICATIONS FOR CROP IMPROVEMENT PROGRAMMES Genetic selection for improved nutritional quality of rice straw- -a plant breeder's viewpoint Gurdev S. Khush , Bienvenido 0. Juliano and Domingo B. Roxas 261 Evaluating sorghumvcultivars for grain and straw yield John McInCire , Jess D. Reed, Abate Tedla, Samuel Jutzi and Yilma Kebede 283 General discussion 305 SESSION 5: RECOMMENDATIONS AND FUTURE PROSPECTS FOR PLANT BREEDING TO MAINTAIN OR IMPROVE THE NUTRITIVE VALUE OF CROP RESIDUES Reports of working groups 309 Recommendations 317 General discussion 321 LIST OF PARTICIPANTS 329 xi SESSION 1 The role of crop residues as feed resources in smallholder crop/livestock farming systems IMPORTANCE OF CROP RESIDUES FOR FEEDING LIVESTOCK IN SMALLHOLDER FARMING SYSTEMS R. E. McDowell Visiting Professor, Department of Animal Science, North Carolina State University, Raleigh, NC 27695-7621, USA INTRODUCTION In the tropics (latitudes 30°N to 30°S) , 40 to 80% of the livestock are associated with mixed crop- livestock farming systems, e.g. Africa 60% (Brumby, 1987, World Bank, 1987). Because of this close relationship between crop and livestock production, animal scientists are highly concerned by plant breeders' efforts to change the distribu tion of plant nutrients to the point that the nutritive value of the crop residues becomes too low for animals to obtain even their maintenance requirements. This reduction in feeding value of grain crop residues has often resulted in low adoption of new varieties by smallholders . Agronomists and livestock scientists both aim at improving the welfare of farmers. However, efforts to improve farm productivity of crops and livestock have often been less successful than anticipated. Even so, African countries in which crop production has increased considerably during the last decade had a corresponding increase in livestock numbers (Brumby, 1987). When projecting farm output the interdependence of crops and live stock must be taken into consideration. On almost all small farms there is a strong interaction between cropping systems and livestock, and this results in poor adoption by farmers of either agronomic or livestock interventions developed in isolation (Hart and McDowell, 1985). This presentation focuses on crop -livestock inter actions, which are important to both agronomists and animal scientists. CROP-LIVESTOCK SYSTEMS There have been a number of efforts to identify and describe farming systems in warm-climate regions based largely on geography (political and physical), climate, cropping pattern and animal output. Seldom has there been focus on crop- livestock relations. Emphasising crop-livestock relations, McDowell and Hildebrand (1980) identified prevailing systems on small, mixed farms in Africa, Asia and Latin America. Ten major systems were identified in Asia: with the exception of swidden ( slash- and-burn) farming, crop residues and byproducts from human food processing provided 30 to 90% of livestock feed. Africa has 10 major systems with 22 subsystems: dependence of live stock on crop residues was high in all 22 sub systems. In Latin America, four major systems were identified: in all except one, (commercial cattle ranching) crop residues provided 30 to 90% of livestock feed. Nearly all systems on the three continents also depended on grazing from fallowed crop lands. The close interdependence of crops and live stock in smallholder systems in the highlands of Kenya is shown in Figure 1. Average farm size is approximately 1 ha and more than 85% of farms have livestock, usually two or more species. The interdependence of crops and livestock is primari ly through dependence of animals on crop residues Figure1.Atrop/lirtotockagr ofltstralo sst■mtommoninhafar stheot t■enprorin ■oK■nya. Floosb■t p0nropsandlitstotka ■1000Mgalofdi ■ ible■ =gy(DE).Histog amssh monthlydistribsttions. mm Crop/LivestockAgriculturalEcosy em Mor0Aug'Sept0D c 50kgyr0 3,800kgyr- 1,200kgyr0l m Fallow 0.80000l0OBho Ol+TW* 4W* it Fencerows ~*MiTfMtmi m Offfarm 002ha0 Precipitation 1800mmyr0' Solar radiation Soilnutr wih Moizta beans eds Maiz*e + beans 0.5ho04 Maizeo 0.2ho0a P£ t0.1ha- J*^ Monthly available UwEJ 24.8k1000 MealDEyr01 kJl Livestock herds Icow 150month calving interval 2sheep 00month lambing interval Feedstorage Mar0Aug'Sept0D c mrMmm Source:Ha tandMcDowell(19N5) Maize Cossova■ 60kgyr0i livewt. cattle 30kgyr ' livewt. sheep Meot^ Milk 00kgyr for feed. Farmers manage individual cropping patterns (intercropped maize and beans, double cropped maize and cassava) to provide food and feed. Each crop contributes feed during various months (histogram, Figure 1). Neither crop nor livestock productivity can be increased without due consideration of the interaction between crops and livestock. Farms depicted in Figure 1 may on occasion hire animal traction for land preparation, but most cropping is by hand. Farmers keep, on average, one cow, two sheep and several poultry using farm and external feed sources, such as grazing or material cut from roadsides and forest. Maize stover is the most important feed. Farmers in this area have made little use of improved maize varieties because their stover yield is low unless fertilizer is applied and the indigestible neutral detergent fibre fraction (INDF) in their stover is higher whether with or without fertilizer. Although crop and animal production can be strongly interdependent, the factors that can influence farmers' decision-making are often more complex (Figure 2). Sands (1983) made an in-depth study of the contributions of animals on 80 farms in two districts of western Kenya (mean size 1.03 ha) . Using a two-dimensional model (household- market and household- farm) , as proposed by McDowell and Hildebrand (1980), two major sub systems requiring labour and capital were charac terised. The solid lines from the crop subsystem to the animal subsystem show high dependence of animals on crop residues and strong dependence of cropping on animals for power in land preparation and fertilizer from manure dropped on fallow land while grazing or manure collected from night -c 2 >5 3 .5 £ 3 "a R (fl j-. 3 -1 5 s « = CM | "*" < Ik. 2 *> Q. y, 0- U — _ V — — * z *• •> O 3 ■a< a n o o •• u.S 3 cj w o a. a ^_ O £> E a i A i£ T e a • * >v tu (* tfl O 2 «* - ftj T> J= C O 2 O s •o? — M — ,& o — o M o 9 a ¥ ILUU ' — • t0 *• °2Iuq■9 a *» a m i- N c • 5 u h X O i/> « c 6 m * 3 UJ jO M•o c u 2.ay < a CO nil o e 2 - •j O %1 2 o * 1 • "2 r 2 co ■w o e.R g 2 CD O CO 5 u. 1 ■ (C 1 o E I u c 0 o u b 2^ 3 0 2 S • 1 fft il a -1£ a s co ,g 1 c •i "a i 0) *z 5 y S a. 2 E o - ° *I 0 5 ir u * 8 M «, • • k. — i_ «n t_ o> « 0— o Q3 "*. O D O O O 01 t O ~2 io o c > m o ^3 Z 2 y 0 s 5 o (N a U 3 k* O 3 C/5 00 E holding areas for composting with inedible crop residues . The solid line between crops and the market indicates the importance of crop sales : grain sales provide over 20% of household income. The broken line from market to crops shows low depen dence on the market for inputs of seed, fertilizer or pesticides. Although annual income from sale of animals or their products equals or exceeds income from crops, the animal subsystem has an unpredictable relation to the market, i.e., sales of milk or animals are erratic. As with crops, purchases of inputs, e.g. animals, feeds or veter inary services, are sporadic. This implies that animals are kept largely for services to cropping, storage of capital, some household food and income and to provide for emergency needs: nevertheless, they are essential to the total farm operation. For systems portrayed in Figure 2, interven tions in either the crop or livestock subsystem would need to be approached cautiously for farmer acceptance and to avoid an unacceptable imbalance, such as less fodder or need of more feed for a crossbred cow. The solid arrow from household to market shows significant off -farm employment, hence availability of labour could be a constraint to adoption of new practices in either subsystem. Obviously, cash flow to the farms is low; there fore, inputs requiring capital will have low acceptance for either subsystem. It is clear that agronomists and animal scientists must work together to increase produc tion from these small mixed farms and that the extent of interactions between crops and livestock must be determined before interventions can be developed. USE OF CROP RESIDUES In developed countries crop residues are largely returned to the soil or, in some instances, may be used for maintenance of beef cattle during the winter (Anderson, 1978; Klopfenstein et al , 1987; Males, 1987). Where only the grain is used, the overall efficiency of utilisation of total energy from a crop such as maize is low. One hectare of maize may yield approximately 30 240 Meal of metabolisable energy (ME) and 620 kg of protein in the grain and stalk (Table 1) . When only the grain is used for human consumption or for live stock feed about 39% of the energy and 20% of the protein are utilised. When the bran and stover Table 1. Production and utilisation of maize. Meal ME01 Protein (kg) Production ha" Grain 19 040 360 Plant 11 200 260 Total 30 240 620 Human or animal feed U.S. Grain 11 735 123 % total 38.8 20.0 Subsistence farms Grain Human consumption 11 735 123 Bran, animal feed 2 810 22 Stover, animal feed Milk 2 580 31 % total 56.7 28.4 1. Megacalories of metabolisable energy. are also used as animal feed, total ME utilisation may be increased to over 56% and protein utilisa tion to 28% (Table 1) . Table 2 shows the high seasonal dependence of small farmers (1.3 ha) in southern India on crop residues (dry fodder) . In this region milk sales are important, hence some purchased concentrates plus brans are used as supplements to maximise intake of the coarse feeds. Dry fodder provides 13% of feed dry matter from August to October, but 52% from January to April. Table 2. Feed sources on mixed farms used for feeding buffaloes and cattle by season in southern India (kg animal" day" ) . Jan- May- Aug- Nov- Apr July Oct Dec Green fodder Dry fodder Purchased concentrates House concentrates Other1' Pasture (h d ) 2.22 2.20 9.06 6.19 5.87 4.02 1.15 4.55 0.89 0.19 0.40 0.44 1.51 0.65 0.40 0.16 0.08 0.34 2.31 3.27 3.31 3.40 3.23 3.46 1. Largely weeds removed from crops or regrowth of rice. 2. Maize or sorghum stover, wheat and rice straws . 3. Brans from preparation of human food. 4. Grasses harvested by women from footpaths, and neighbouring fields. 5. Communal grazing with realised intake of < 1 to 3 kg of dry matter per day. 10 African pastoralists are highly dependent on crop residues from their own small plantings or from crop farms to supplement grazing during the dry season. The deficiencies of grazing in northern Nigeria, a central district in Botswana and the Machakos District in Kenya are shown in Table 3. Estimates of intake from grazing by 250-300 kg cattle are expressed in relation to animal needs for body maintenance (1.0). In northern Nigeria, grazing normally provides sufficient energy from June to October for a cow to gain up to 1.0 kg per day (July to September) but grazing cannot meet the animal's energy needs from December through May, resulting in serious weight losses. Fluctuations in feed quality and quantity lead to low net weight gains of about 70 kg a year. In Botswana the feed is deficient for only about 4 months but grazing and browsing in Botswana requires greater energy expenditure than in Nigeria. Even so, animal gain could reach 90 kg per year. If sufficient grazing is available, there is less need for supplementary feeding in Kenya than in Botswana or Nigeria (Table 3) . Expected animal gains would exceed 110 kg per year (Nsibandze, 1982). Average rainfall in the three areas is approximately the same. Its distribution has a marked effect on the grass species and their nutritive value, which is highest in Kenya, some what lower in Botswana and least in Nigeria. In Kenya and Botswana browse adds significantly to feed quality and quantity. In Nigeria, heavy rains over a short period lead to rapid growth and maturity of grasses followed by marked decline in quality. As pointed out by Wilson (1982) and others, supplementary feeding is essential in much of the subhumid and semi-arid areas of West Africa. The need for manure on cropped areas and 11 Table 3. Estimates of monthly energy intake by 250-300 kg cattle on rangeland grazing in three areas in relation to maintenance needs . Central Machakos Northern District District Month Ni.geria Botswana Kenya January 0.8 2.1 1.4 February 0.7 2.0 1.2 March 0.6 1.7 1.5 April 0.6 1.4 1.9 May 0.5 1.2 2.0 June 1.5 1.0 1.6 July 2.3 0.8 0.9 August 2.2 0.7 0.8 September 2.0 0.6 1.0 October 1.5 0.6 1.5 November 1.2 1.6 2.0 December 0.9 2.1 1.6 Mean 1.23 1.29 1.45 Average dai iy weight ga in (kg) 0.20 0.24 0.30 Source: Adapted from McDowell (1985). 1. Example: January, northern Nigeria 250-300 kg cow has intake 80% of energy needs for body maintenance thereby losing weight but in July intake is 230% of maintenance needs when weight gain or milk yield can be high. 2. Rainfall 450-500 mm; 97% from late May to mid- September. 3. Rainfall 400-500 mm; 95% from late November to mid-May. 4. Rainfall 500-550 mm; long season March-June and short rains October-December. 12 the pastoralists ' need for feed leads to strong interdependence between crop farms and pastoral ists (Wilson, 1982). An average pastoral unit requires about 10 breeding cows, a breeding male and associated stock for subsistence needs (Brumby, 1987). These animals may use about 100 ha of rangeland provid ing approximately 10 500 kg of total digestible nutrients (TDN) per annum, which is far below needs. In northern Mali average rangelands in normal years will provide about 50% of livestock needs, hence crop residues must be used to avoid large weight losses in the dry season. Data have not as yet been collected to deter mine whether the interrelationships between crop farmers and pastoralists in West Africa have influenced the adoption of new varieties of grain crops due to possible changes in yield and quality of crop residues, but ILCA researchers reported low acceptance of high-yielding varieties of cow- peas in northern Mali because of low forage yield. Concerns have been expressed in northern Nigeria and other areas over the rapid expansion of maize production, because maize matures earlier than sorghum or millet, while grazing is still reasonably good. As a result, the quantity and feeding value of maize stover is markedly lowered by weathering before it is needed for feed. FARMER DECISION-MAKING 1 . Choice of crop Subsistence farms attempt to sustain about 4.5 people per household, each needing about 200 kg of grain per year. The farm must thus produce a 13 total of 900 to 1000 kg of grain a year. Farm size is 1.5 ha, with 1.0 ha planted to maize and beans, 0.3 ha to wheat and 0.2 ha to sorghum. Using local varieties and low inputs, maize yields 600 kg of grain, beans 150 kg, wheat 200 kg and sorghum 150 kg, giving a total yield of 1100 kg, about basic human food needs. There are two cows, one bullock, one calf, two sheep and three goats. Yield of wheat straw is about 200 kg (1:1 ratio with grain) (Anderson, 1978) and maize plus sorghum stover 3450 kg (1:5 or 6 ratio to grain yield, in local varieties). Thus, the total crop residue yield is about 3650 kg, which provides approximately 150 days of feed. This, supplemen ted with off- farm grazing, could maintain the livestock. Cash flow is low so the farmers want to reduce the maize land to 0.5 ha and add 0 . 5 ha of cotton as a cash crop. A new variety of maize is used and fertilizer applied, giving a yield of 1000 kg of grain. Of this, 200 to 300 kg is sold to pay for purchased inputs. The ratio of maize stover to grain yield is reduced from 1:5 or 6 to 1:1.5 or 2, hence maize stover yield is reduced to 2000 kg. The cotton provides no feed except weeds, hence total crop residue for dry season feeding is reduced to around 2500 kg, resulting in only 100 days of feed. The cattle fare less well because the digestibility of the maize stover declined from 52-56% (sufficient energy available for maintenance needs plus some for production) to 42-45% digestibility (sub -maintenance needs in energy) (Sands, 1979). The farmer must choose between reducing stock numbers, which is unattrac tive due to loss of prestige and savings, purcha sing feed for livestock, relying more on off -farm grazing or returning to the traditional system. Other farmers have followed a similar procedure 14 thereby placing greater pressure on communal grazing. In the second year nearly 50% of the farmers withdraw from the maize -cotton programme, to the consternation of extension agents. 2. Change crop residue management Crop residues are low in protein and phosphorus, marginal in calcium and high in fibre and lignin. As a result, digestion is slow, rate of passage is low and voluntary intake is limited, e.g. ad libitum intake of sorghum stover is 43% less than that of hay. Intake may be increased about 20% by chopping the residue (Anderson, 1978) . Maize or sorghum may be cut and stacked or shocked to reduce leaf loss from leaching or wind damage. Research has shown that stripping the lower leaves (below the ear on maize or the lower half of sorghum) increases feeding value. Topping maize after the grain has nearly matured also helps to preserve forage quality. Although these procedures improve feed quality, farmer acceptance has been low because of low visibility of return to the extra labour required. Assembling or storing crop residues may be a necessity where cropland is highly fragmented, such as often occurs in India; where the household is dependent on manure for fuel --India and Ethiopian high lands--; or where marauding animals have access to crop residues during the off-crop season. When these elements are not pressing, farmers prefer to graze the residues to reduce labour for storage or transport of manure to the fields . Preservation of crop residues is, however, attractive where high-protein concentrates, such as cottonseed cake or grain brans , are available 15 at modest prices. With supplement, intake of residues may increase 20 to 30% (Conner and Richardson, 1987; McDowell, 1985). Farmers generally accept supplementation as an initial move to increase milk output or to fatten cattle or sheep (World Bank, 1987). 3 . Chemical treatment Other papers at this workshop deal with this issue. In farmer decision-making, suffice it to say that, although research results show promise, acceptance on resource -poor farms is slow due to costs (labour and capital) and risks. Chemical treatment could be more attractive if it were complemented with modifications in the farming system. Forage crops have not received much attention in cropping systems research (Gibbs and Carlson, 1986). From the example given in section 1 above, production systems and crops need to be developed that will best meet the dual- purpose needs of smallholders . Including forage legumes in the crop rotation can increase the yield of the subsequent crop and sustain soil fertility, and such rotations need investigation. Indirectly, forage legumes would increase returns from crop residues through higher intake and more efficient digestion. Availability of good quality forages for supplement may, however, lessen the attractiveness of chemical treatment. 4. Change the animal In recent years a frequent recommendation is for smallholders to concentrate on goats and sheep instead of cattle or buffalo. The advantages of 16 low investment, early maturity and better breeding efficiency are most often cited. This recommenda tion makes the assumption that all four species are equally adept in the utilisation of crop resi dues , but this is not the case (Demment and Van Soest, 1983; Hart and McDowell, 1985; McDowell, 1987a; 1987b; McDowell, 1986; McDowell and Wood ward, 1982) . Feeding strategy is an important feature in assessing suitability of animal species. The comparative digestive strategies of goats , sheep and cattle are given in Table 4 . Figure 3 portrays how selective feeding behaviour influences whether a given animal species is widely dispersed or clustered in certain areas because of prevailing feed resources. The two major types of Bubalus bubalis (swamp and riverine buffalo) are probably the best users of crop residues among domestic livestock. Buffalo are grazers with low selectivity (Figure 3); they have a wide muzzle, large gut capacity and a greater extent of fermentation in the rumen than cattle. The last two features result in slow passage of food through the digestive system. The buffalo is therefore an effective user of high fibre feeds. Their major habitat, the paddy rice area of Asia, verifies their ability to use rice straw. Their best niche appears to be as users of crop residues or to provide some returns from grazing marsh areas. Their efficiency on high- quality forage is lower than that of cattle. Cattle are classed as grazers with relatively low selectivity but are slightly more selective than buffalo. Their metabolic rate is lower than that of goats or sheep and their rumen retention time is longer, resulting in greater ability to digest fibre. The vast bacterial population in the rumen of cattle is a significant source of 17 Table A. Comparative digestive strategies of goats, sheep and cattle. Characteristics Advantage Limitation Goat Browser Plant differentiation (morphological and seasonal) Low utilisation of total blomass Rapid passage Low Mj^ Grazer Higher Intake possible, rapid passage of low- quality feed Allows greater diet selection Sheep Less travel energy needs, better use of total blomass Intermediate rate Better fibre digestion of passage Intermediate M^ Permits higher cellulose fermentation Small body size Small absolute intake More time required for eating High energy cost, Increased maintenance requirements Diet limited to graze plants, plant differentiation not fully utilised Forced to waste effort on low-quality feeds Decreased apparent digestibility High MR/GC2 Cattle Grazer High use of plant blomass Diet limited to graze plants, plant differ entiation limited Slow passage High Mt Large body size High fibre digestion High cellulose fermentation Low MR/GC, long legs, move rapidly Forced to waste effort on low-quality feed Decreases apparent digestibility Mouth too large for plant differentiation 1. M, value is that part of the faeces endogenously produced by the animal besides the undigested feed residue. 2. MR/GC - ratio of basal metabolic rate to gut capacity. Source: McDowell and Woodward (1982). 18 Figure 3. Free-roving animals will congregate in areas where feed is available and suits their needs. In tropical areas, animal size plays an important role in feeding behaviour. Small animals must be highly selective in choosing grasses and browse. This figure shows where familiar and exotic animals are found based on their feeding behaviour and pre ferredfeed resources. Arrows indicate crossover may occur. Highly selective i o c a> .o en c -o ID Leost selective G ross ♦- -•-Browse Source: Adapted from Demment and Van Soest (1983). protein. Thus cattle can survive on a diet of poorer quality grazing than can goats or sheep. Cattle can browse to a limited extent but their broad muzzle and slow bite rate does not make them effective browsers. Their absolute intake requirements are so great that there is generally 19 insufficient high quality feed in tropical environments to sustain high levels of perfor mance. There are morphological traits in the two species of cattle, Bos indicus (zebu or humped types) and Bos taurus (European or non-humped types) that can be significant in utilisation of crop residues. Bos indicus types have a longer, narrower head and smaller muzzle. They have near ly 25% less digestive capacity per unit of body size than Bos taurus types, which forces them to be slower and more selective feeders. On range- lands with shrubs for browse, Bos indicus will select a higher quality diet but will utilise less of the total forage dry matter. For example, zebu heifers grazing at the rate of 2.5 head per ha on improved grass pastures in Puerto Rico utilised 18.7% of the total DM while Holstein heifers of similar age and at the same stocking rate used 31.2% of the DM. A conclusion is that the feeding behaviour of zebu cattle is more responsible than other adaptation features for its high numbers in the tropics (Hart and McDowell, 1985). This fea ture is most important for grazing but is a limitation for zebu in use of crop residues. In India, Pakistan and other parts of southeast Asia, a buffalo cow fed ad libitum rice straw will maintain body weight and produce 1.0-1.8 litres of milk per day while local cattle will lose weight. Goats are among the most selective of the intermediate feeders (Figure 3) and can use a wide range of plants. Their M^ (endogenous and microbial fraction of the faeces) values are lower than those of cattle and sheep (Table 4) because they generate less cellulytic bacteria in the rumen, which lessens cellulose digestion. The feeding strategy of goats is to select grasses when protein content and digestibility are high but to shift to browsing when leaves, bark and 20 fruits have better nutritive value. Their small mouth and prehensile lips enable them to gather small leaves and flowers . Performance of goats may be low and mortality high on an exclusive diet of dry- season grasses in the subhumid zone but they will thrive in the same zone where there is a mix of browse, while cattle may be hard pressed to survive. Overall, goats are not good users of straws and stovers unless they are given an opportunity for high selection and receive some supplementary protein as bran or browse. Goats may die on an all maize stover diet or when penned on dry, mature tropical grass. Thus, goats have unique feeding strategies which can be employed to complement sheep or cattle for fullest use of certain ecosystems, but where crop residues are the main feed source goats are at a disadvantage. Sheep tend to be mainly grazers but, as for goats, their body size requires they feed selec tively. They are able to digest fibre effectively but on a diet mainly of crop residues, such as straw, they have the disadvantage of being forced to ruminate in order to clear their rumen; therefore, straw or stover gives low nutritional benefit for the energy expended. It is more difficult to relate feeding behaviour to area of concentration for sheep than buffalo, cattle or goats because they have high utility for meat and fibre as well as importance as a feature of the Moslem religion. They usually complement other species in maximising use of ecosystems. McDowell and Hildebrand (1980) showed that even though the number of small ruminants per farm was low, most had cattle, goats, sheep and, in Asia, buffaloes. This indicates that: a) farmers are aware of the limitations of each animal species; b) they know the complementarity of 21 species in utilisation of available resources; and c) they recognise that each species has a well defined function in the farm enterprise. It appears that for much of Africa cattle will tend to dominate as the best overall user of feed resources but in planning agronomic or livestock research strategies, small ruminants should be considered as part of almost all farm systems. FUTURE It is hoped that plant breeders will recognise a desire on the part of animal scientists to consider modifications in plant selection to maintain as high an animal utility as possible; that it will be agreed that further research on chemical treatment of crop residues may be warranted; and that the animal nutritionists will agree to move forward as rapidly as they can on standardisation of methodology for assessment of animal utility of crop residues and forages. Hopefully the workshop will also explore the broader issues of production systems. We must appreciate that improvements in the feeding value of crop residues, whether by plant breeding, chemical treatment or both, will provide relative ly low returns for smallholders, possibly 10-20%, in increased returns from animals. Predicted acceptance at this level of change will at best be modest because there are still problems of malnu trition among the animals. Improvements in straw quality could increase energy availability signi ficantly but will do little to increase the availability of protein and phosphorous, which are in short supply in smallholder systems. 22 For ruminants such as cattle to express their full genetic potential for performance, the apparent digestibility (AD) value or the TDN content of the entire ration should exceed 70% on a dry weight basis. When AD is 60% performance will be intermediate and at 55% AD, production will be approximately 10 kg of milk per day or 0 . 5 kg weight gain per day. The minimum range in AD to assure body maintenance needs is 42-45%. At lower AD levels, animals lose weight. In the average feed supplies on mixed crop/livestock farms depending on crop residues for more than 100 days of feeding, around 10% of the total has AD 55% or more, 50% has an AD of 45-50% and 40% has an AD of less than 40%. Increasing the mid-range (50-55% AD) by 10 units will increase animal output by 20-40% provided total animal biomass remains constant. If the workshop participants accept ILCA's long-range strategy on "thrusts" in research on milk and meat from cattle and small ruminants, animal traction and animal feed resources (ILCA, 1987) , a needed focus in this exchange is much closer collaboration with the plant sciences including soils and agroforestry . Participants should be planning for research of ILCA and NARS on identification and development of varieties and commensurate production systems of leguminous and dual-purpose crops which can produce high- quality food and fodders. ILCA's main thesis for shifts in strategy is the observation that: In many cases livestock and livestock products are the most important source of the cash income of subsistence farmers. Small improvements in live- 23 stock productivity quickly result in important income changes and in the availability of funds to improve the subsistence- cropping patterns that characterise smallholder agriculture . (Brumby, 1987). ILCA's strategy strongly suggests that research on production systems to meet the dual- purpose needs for smallholders will mean greater flexibility for all production systems, with or without livestock. Demonstration by ILCA researchers that rotation of forage legumes with food crops enhances yield of the subsequent crop and sustains soil fertility is most encouraging. Research on Vertisols in Ethiopia further shows ILCA's commitment to increasing total farm output. REFERENCES Anderson D C. 1978. Use of cereal residues in beef cattle production systems. Journal of Animal Science 46:849-861. Brumby P J. 1987. Livestock: A sector policy paper. World Bank, Washington DC, USA. Conner M C and Richardson C R. 1987. Utilization of cotton plant residues by ruminants. Journal of Animal Science 65:1131-1138. Demment M W and Van Soest P J. 1983. Body size, digestive capacity and feeding strategies of herbivores. Winrock International, Morrilton, Arkansas, USA. Gibbs M and Carlson C (eds) . 1986. Research imperatives revisited, an international conference held at Boyne Highlands Inn, 13-18 October, 1985, and Airlie House, 11-13 December, 1985. 24 Hart R and McDowell R E. 1985. Crop/livestock interactions as determinants of crop and livestock production. Cornell International Agriculture Mimeo 107, Cornell University, Ithaca, NY. ILCA (International Livestock Centre for Africa) . 1987. ILCA' s Strategy and Long-Term Plan. ILCA, Addis Ababa, Ethiopia. Klopfenstein T, Roth L, Rivera S F and Lewis M. 1987. Corn residues in beef production systems. Journal of Animal Science 65:1139- 1148. Males J R. 1987. Optimizing the utilization of cereal crop residues for beef cattle. Journal of Animal Science 65:1124-1130. McDowell R E. 1985. Case studies on livestock in warm climates. Instructional Materials, CAWFI , Department of Animal Science, Cornell University, Ithaca, NY, USA. McDowell R E. 1986. An animal science perspective on crop breeding and selection programs for warm climates. Cornell International Agriculture Mimeo 110. Cornell University, Ithaca, NY, USA. McDowell R E. 1987a. Ethical aspects of food aid policies for third world countries. In: Ethical aspects of food, agriculture and natural resource policy. Proceedings of a workshop held at the University of Kentucky, Lexington, June 1987. University of Kentucky, Lexington, Kentucky, USA. McDowell R E. 1987b. Matching the animal to the environment: Cattle. In: J E Moore, K H Quesenberry and M W Michaud (eds) , Forage - livestock research needs for Caribbean Basin. Caribbean Basin Advisory Group, University of Florida, Gainesville, Florida, USA. pp. 109- 118. 25 McDowell R E and Hildebrand P E. 1980. Integrated crop and animal production: Making the most of resources available to small farms in developing countries. Working papers: The Rockefeller Foundation, New York, NY, USA. McDowell R E and Woodward A. 1982. Concepts in animal adaptation: Comparative suitability of goats, sheep and cattle to tropical environments . Proceedings of the 3rd International Conference on Goat Production and Disease. Dairy Goat Journal. Scottsdale, AZ, USA. pp. 387-394. Nsibandze E P. 1982. The economics of cattle ranching in Machakos District Kenya. M.S. thesis, Cornell University, Ithaca, NY, USA. Sands M W. 1979. Variation in the nutritive value of overripe maize stover. M.S. thesis, Cornell University, Ithaca, NY, USA. Sands M W. 1983. Role of livestock on smallholder farms in western Kenya: Prospects for a dual purpose goat. Ph.D. thesis, Cornell University, Ithaca, NY, USA. Wilson R T (ed) . 1982. Livestock production in Mali. ILCA Bulletin 15. ILCA, Addis Ababa, Ethiopia. World Bank. 1987. West Africa agricultural research review. World Bank Western Africa Projects Department, Washington DC, USA. DISCUSSION prskov: You suggested that zebu cattle are unlikely to survive on rice straw, yet in Bangladesh zebus are kept on this material. McDowell: I doubt that they are kept exclusively on rice straw. Zebu cattle retain feed in the digestive tract for less 26 time than do buffaloes. As a conse quence their digestive capacity is 25% less . This means that they have to be more selective feeders and receive a more constant feed supply. Little: There is generally no clear relation ship between digestibility and intake for most feeds in the tropics, and therefore no direct relationship between increases in roughage digest ibility and livestock performance. Nevertheless we generally consider that a digestibility of 50% leads to an intake of around 50 g kg" W ' day"1. McDowell: I have no counter to your statements. 27 THE AVAILABILITY OF CROP RESIDUES IN DEVELOPING COUNTRIES IN RELATION TO LIVESTOCK POPULATIONS Vappu Kossila Institute of Animal Production, Finnish Agricultural Research Centre, SF- 31600 Jokioinen, Finland INTRODUCTION The need to improve utilisation of crop residues in developing countries has received considerable attention in recent years , but there have been few studies on the availability of fibrous crop residues in relation to their potential for feeding livestock. The availability of crop residues is closely related to the farming system, the crop produced and the intensity of cultiva tion. The potential for use of crop residues as livestock feed is greatest in integrated crop/ livestock farming systems. Where crop and live stock production are segregated, most crop residues are wasted. Crop residues are also wasted or used for non-feed purposes in many smallholder crop/livestock systems in developing countries . In this study the amounts of crop residues (not including agro- industrial byproducts) available on farm have been estimated. Fibrous crop residues from cereals (straw, hulls, husks, cobs, awns, chaff etc) are the most important. Their use as livestock feed is limited mainly to ruminants. More detailed presentations of the methods used and global data are presented elsewhere (Kossila, 1984; Kossila, 1985). 29 METHODS The following procedure is an outline of methods used to estimate the availability of crop residues in relation to livestock numbers: 1. Define the area of study (single farm, village, county, province, country, group of countries, region, world) and estimate the area of cropped land. Farm and village -level studies should be conducted before starting development projects aimed at introducing improved livestock production technology into smallholder farming systems in developing countries . 2. Select the crops to be included in the study, estimate the crop yield per area per annum and determine the yield of crop residues on the basis of grain yields. Examples of multipliers used for converting yield of cereal grain into yield of crop residue are given in Table 1. Multipliers for other important crops are given in Table 2. These are highly variable and should be determined regionally. 3. A livestock census should be taken if no reliable data are available. Livestock numbers should be converted into livestock units (LU) . The researcher needs to decide which livestock unit to use: the tropical livestock unit is a 250 kg bovine at maintenance, whereas the LU used in most developed countries is a 500 kg bovine at maintenance. The choice should be clearly stated and not confused. Some examples of multipliers used to convert livestock numbers into LU are given in Table 3. However, 30 H1n 60 4X oE 1o 14* O893 ETUeaOQ Eo 4X sl oT O893 Qol adojng 1X oX oZ Eo l» o* e4[oV oooo 1 oZoo o1/ oo qjnoo eOfJ"U4V zo Eo oE oT O^ o» 1I oX oZ oo o1? 1** Tfoiajv Oo 1o l1 1o oo o XatJleg az1«w 1"1oW lfBa1pax4fw sa-[;1]uenb^onpoprXqsnoaqij03p^aTXut 9jeaaaoiib uodp sns^a ^d4 inH\afq^I Table 2 . Multipliers used in converting various commodities into dry-matter yields of their fibrous byproducts . Commodity Multiplier Sugar-cane (fresh) 0.25 Roots and tubers (fresh 0.20 Pulses (dry) 4.00 Nuts (dry) 2.00 Oilseeds and oilplant residues (dry) 4.00 Vegetables, melons etc (fresh) 0.25 Fruits, berries (fresh) 0.40 comparisons of availability of fibrous crop residues per LU should be interpreted with care because of large differences among ruminants in feeding behaviour and nutritional physiology (Van Soest, 1982). RESULTS The quantities of fibrous crop residues (cereals, sugar-cane and other crops) in relation to live stock numbers by country are shown in Figure 1. In 1981, the average estimated amount of fibrous crop residues per LU was 2811 kg, with the highest regional average (5480 kg) in North and Central America and the lowest average (1019 kg) in Oceania. Quantity of fibrous crop residues increased from 1970 to 1981 by about 36% (Figures 2 and 3) whereas the number of grass eaters (i.e. ruminants) increased by only 10%. 32 N o 3 N r^ eo rH 0 0 GO iH 0 fH iH iH o o N 0 u 3 M vo r» N 0 0 f-t N r^ oo 0-* N N d S <3 I H J « 4J i« 0 M « 3 !B < u « 3 CO O Cu i/) O 33 >01 01-o: o60 fr-Z Z-l D (oJ"JB"ooBJSJOQTJ d\Qj)o"tipio"Xjl Uenf) (JVJAU.nloJ")D"SSVu8fo liunyDoiosAi]1h!f\Qosuuor)ig(,/wpj oM" (i}oosl*tiod* sjfipS"npio"jd jDon jql /ouoi)3lipo j•\an8 Figure 2. World production ofcereal crop residues, 1970-81. Production (million t DM) 1200 100 100 ,• Maize 1000 900 - 800 - 700 600 500 - 400 300 o _u» — 4^ «* ~o ~ "~ ?00 -| - .' 'rrr-'Aj .'% Wheat o Rice paddy , Sorghum Barley Mixed groin Millet :r.". •^••TR/» Oats "-•.vRye . .Buckwheat i i i i i i i—i 1 r 1970 71 72 73 74 75 76 77 78 79 80 81 Year 35 Figure 3. World production offibrous residues from pulses and other crops, 1970-81. Production (million t DM) 600 500 400 - 300 200 100 -- Pulses ..— Oil plants , **' Sugor- . ■•• cane — Roots a tubers Nuts —i 1 1 1 1 1 1 1 1 1 1 1970 71 72 73 74 75 76 77 78 79 80 81 Yeor In many countries the amount of crop residue exceeds the amount that can be used. These include the USA, Canada, most European countries, a few Near Eastern countries, a belt of countries from Mozambique to the southwest coast in Africa, China, Korean PDR, Korean Republic, and most countries and islands of Southeast Asia. Many 36 other countries have a low ratio of available crop residues to grass-eater LUs . These include most countries in North, East and southern Africa and many countries in the Middle East. In 1981, Africa had about 12% of the world population of grass eaters but produced only about 8% of the world's fibrous crop residues. The residues in greatest supply were maize (95.7 million tonnes), sorghum (55.2 million tonnes) and millet (51.4 million tonnes). Most countries in sub-Saharan Africa with a low ratio of crop residues to LUs have large areas of arid to semi-arid rangelands, large livestock populations and relatively low production of cereals (Table 4) . Countries with a high ratio were mainly in the humid zone of West Africa where cereal yields are higher but cattle populations are severely limited by trypanosomiasis (Table 4) . CONCLUSION Large quantities of fibrous crop residues are already used as animal feed in many developing countries. There are also many areas in developing countries where ruminant livestock starve due to lack of feed. However, globally, it is apparent that cereal production has increased at a greater rate than livestock numbers over the last 10 to 15 years. These trends indicate that research should be strongly directed towards improving utilisation of fibrous crop residues as livestock feed. 37 Table 4. Quantity of fibrous crop residues per grass -eater LU, sub-Saharan Africa, 1981. Quantity (kg DM LU"1) Countries <600 Botswana, Ethiopia, Madagascar, Mauritania, Namibia, Somalia 600-1999 Angola, Central African Republic, Chad, Guinea, Kenya, Lesotho, Mali, Sudan, Tanzania 2000-3999 Burkina Faso, Benin, Cameroon, Cape Verde, Comoros, Gambia, Guinea Bissau, Niger, Uganda, Senegal, Swaziland, Zambia, Zimbabwe 4000-6999 7000-10 000 Burundi, Congo, Ghana, Malawi, Mozambique, Nigeria, Sierra Leone , Togo Gabon, Cote d'Ivoire, Liberia, Rwanda, Zaire REFERENCES Kossila V. 1984. Location and potential feed use. Chapter 2 in: F Sundst^l and E Owen (eds) , Straw and other fibrous by-products as feed. Elsevier, Amsterdam, the Netherlands, pp. 4- 24. Kossila V. 1985. Global review of the potential use of crop residues as animal feed. In: T R 38 Preston, V L Kossila, J Goodwin and S B Reed (eds) , Better utilization of crop residues and by-products in animal feeding. 1. State of knowledge . FAO Animal Production and Health Paper 50. Food and Agriculture Organization of the United Nations , Rome . pp. 1-13. Van Soest P J. 1982. Nutritional ecology of the ruminant. 0 & B Books, Corvallis, Oregon, USA. DISCUSSION Thomson: Cotton crop residues are important in Mediterranean countries such as Syria and Egypt. Could you comment on the availability and use of this material? Kossila: Cotton residues were included in my calculations but much more information is needed on the amounts available for animal feeding compared relative to other uses. 39 THE IMPORTANCE OF CROP RESIDUES AS FEED RESOURCES IN WEST ASIA AND NORTH AFRICA Thomas L. Nordblom Farm Resource Management Program, International Center for Agricultural Research in the Dry Areas (ICARDA) , P.O. Box 5466, Aleppo, Syria INTRODUCTION The importance to farmers of crop residues for feeding ruminant livestock has long been neglected, if not falsely maligned, by scientists who define their success only in terms of grain yield per hectare. The error in this neglect is proven when a farmer rejects an "improved" cultivar because of its clearly inferior straw quality. This paper argues that we are really dealing with joint products of cropping in North Africa and West Asia, rather than simply incidental residues. Ruminant livestock add value to and stabilise many farming systems by providing means for storing wealth and for marketing large parts of the farm's crop residues. High-quality crop residues are in short supply in this region. Well-directed plant breed ing, in collaboration with animal nutritionists, may be the surest and most economical path to enhance these important feed resources: new cultivars which, from the farmers' viewpoint, are truly "improved". 41 JOINT PRODUCTS OF CROPPING The farming systems approach to research requires us to look at problems and evaluate possible solu tions from the viewpoints of farmers. In much of North Africa and West Asia, when farmers sow their crops they expect to get feed for their livestock at harvest (and sometimes before), and this expec tation is clearly part of the reason for growing the crop and managing it in the ways they do. In economic terms, the livestock feed and the grain are considered by many farmers as "joint products." In some cases, from the farmers0 view point, the market value of the harvested straw from a field equals the value of the grain: e.g. lentil straw in Syria (Nordblom and Halimeh, 1982), and wheat straw in Egypt (Sallam et al , 1986). These are, of course, not representative of all straws in all countries: the point is that grain is neither the only, nor always the main, reason for growing a crop in this region. One would like to have a simple term that captures the sense of "all those joint-products of cropping which go for livestock feed and which are not grain." Finding no such word, I will stick to "crop residues for livestock." This recognises that other greater or lesser proportions of the non- grain biomass are shattered, trampled, ploughed under or burned in the field, hauled away for use as fuel, in manufacturing (e.g. for paper or press board) or for animal bedding. There is even competition between use of crop residues for livestock versus their use to main tain soil organic matter balances and stabilise crop productivity, particularly where soil erosion is a threat (Anderson, 1978) . This has been 42 flagged as a serious problem in the drier farming areas of Syria where the livestock have been winning the competition and the soils losing (Jaubert and Oglah, 1985). Organic-matter levels in these soils, after many years of almost complete removal of crop biomass, are very low (Cooper et al, 1987). Research is now underway at ICARDA to determine the effects of various stubble management and tillage practices on soil structure and stability. Water infiltration rates and water-holding capacities are aspects of special interest. Control of erosion and sustained levels of productivity are the goals . Even though standing stubbles can be sold for grazing, the loss of some of these fees may be more than compensated by long-term sustainability of crop production if stubbles can be managed to the soil's best advantage. The somewhat derogatory terms, "crop residue" and "agricultural waste" must have originated in the temperate climates of northern Europe and the British Isles. In a review of alternative practical methods for exploiting cereal straws, as fuel, feed and fertilizer, Staniforth (1982, p. 1) stated that: the use and disposal of a huge and growing surplus of straw presents British agriculture with one of its most serious problems . It is easy to understand this European perspective on crop residues as an over-abundant obstacle to clean tillage and clean air. Crop residues are often difficult to deal with: scattered over the fields after harvest, they are invariably bulky, awkward and costly (per unit of weight or value) to collect, transport and store. 43 In a global review of potential uses of crop residues as animal feeds, Kossila (1985) pointed out that countries with the highest ratios of "grain eating" to "grass eating" livestock also tend to have the highest productions of fibrous crop residues relative to numbers of "grass eaters." In Europe, "grain eaters" (in 1981) amounted to nearly 34% of total livestock units; in contrast, for the majority of Middle Eastern countries, "grain eaters" comprised less than 5% of total animal units (Kossila, 1985, pp. 5 and 8) In drier and warmer rainfed farming areas of North Africa and West Asia, farmers' perspectives on crop residues are often fundamentally different from those in Europe. Here, crop residues are seen by farmers as highly desirable joint products of cropping. Cropping intensities (and crop yields) in these rainfed systems are low, with gaps of several months between harvest of one crop and sowing of the next. This often coincides with the rainless summer months, affording considerable flexibility in handling crop residues in the field and allowing time for this to be done by labour- intensive methods, using labour of low opportunity cost (i.e. of women and children). As in Europe, however, crop residues in this region are bulky and expensive or impossible to transport (e.g. stubbles). These materials are always cheapest in the places where they are produced. The demand for their use as livestock feeds is derived from the demand for animal products and the other reasons farmers maintain livestock. The existence of abundant crop residues can create an economic niche for ruminant livestock in the area. 44 Several cases of "joint products," which are not strictly "after harvest residues," should be mentioned because they are part of the bio- economic context. When Pakistani farmers sow wheat, they expect to take two or more hand- cuttings of the vegetative growth for livestock feed before allowing the grain crop to mature (ICARDA, 1987, p. 18). In northeast Syria, barley crops in the green stage are grazed by sheep in winter, then allowed to mature to produce grain and straw (Nordblom, 1983a) . In Egypt maize leaves are stripped from plants before harvest (Soliman et al , 1985). There is also the flexibility to use grazing ruminants to harvest a poor crop in a year when rains fail, where the expected value of the harvested crop, minus the harvesting cost, is less than the value of the crop for direct grazing (Nordblom, 1983b; Mazid and Hallajian, 1983). This practice is widespread in northern Syria (Somel et al , 1984) and south east Turkey (Yurdakul et al , 1987), with the proportions of farmers doing this varying from district to district and from year to year, depending on crop and pasture growth and on cost/ price conditions. Often there are distinct tradeoffs between the options- -green forage, grain and crop residues following harvest- -in terms of quantity, quality and time of availability (Miller et al, 1979, p. 40) . SHOCK ABSORBERS FOR FARMING SYSTEMS Ruminant livestock provide the only means to capture economic value from many pasture resources and crop residues. They are flexible in dietary inputs and levels of output performance, in terms 45 of fertility and rates of milk and meat production. They are mobile and may be trekked to the various grazing sources where and when they are cheapest: around the farm, to the roadsides, to native pastures etc. Their flexibility includes the important capacity to gain weight when feed is good and cheap, then metabolise the stored fat to survive periods when feed conditions are poor. The ability of ruminants to utilise many combinations of pasture, crop residues and concentrate feeds, and to accept changes in these through the seasons of the year and between years , is a great advantage. This allows farmers to use the cheapest available feeds consistent with desired performance. At many sites, these combinations alter from year to year as conditions change (Mazid and Hallajian, 1983; Nordblom, 1983a and 1983b; Mazid et al, 1984). The key role of crop residues is in the maintenance diets of breeding stock: diets for lactation or work require higher energy concentration, as do fattening diets. In Syria, for example, crop residues form the main diet of breeding sheep flocks, with concentrate feeds (mainly barley grain) added at lambing and during lactation (Jaubert and Oglah, 1985; Nordblom and Thomson, 1987; Nordblom, 1987; Thomson, 1987). When prices for slaughter animals or dairy products are high relative to grain prices , farmers are tempted to increase livestock production by adding grain to the diet. For the farmer, grain in fattening and dairy diets can be highly economical (Brokken et al, 1980; Heady and Bhide, 1984) and, because of the demand for grain by dairy and fattening enterprises, surplus grain 46 production and storage capacity is encouraged, often well beyond that needed for direct human consumption. When grain for human consumption is in short supply, reflected in high prices relative to dairy products and meat, livestock diets may be shifted towards lower energy maintenance levels and away from grains. In emergencies, central governments may intervene to accelerate this shift. Livestock may also be sold for slaughter or for transport to areas with cheaper feed. Thus, the grain that would have gone to produce high value meat or dairy products can be diverted quickly to direct human consumption, serving a crucial role for human survival in emergencies (Sarma, 1986, p. 50). The crop residues which are jointly produced with the extra crop areas add to the ease with which grain can be diverted rapidly from livestock to human consumption. Among the world's developing regions, North Africa and the Middle East have the highest projected growth rate (6.1% annually) in the use of major food crops as livestock feed. Human consumption of base staples is expected to grow by only 2.5% annually to the turn of the century, just less than the projected rate of population growth: livestock and poultry are expected to take larger shares of per caput use of base staples as higher incomes are achieved (Paulino, 1986, p. 40). According to Sarma and Yeung (1985, p. 57) demand for feed and fodder will increase rapidly in the coming decades, encouraging more intensive land use and more efficient use of crop residues. Finally, livestock often serve as the store of farmers' wealth: liquid, mobile, prestigious and more secure than other forms of savings in 47 many parts of the region. The combined flexibili ties of ruminant livestock, recognised since antiquity, means they serve as reliable "shock absorbers," to provide important physical and economic cushioning, thereby stabilising and enriching the quality of life in many farming systems. It is in the context of such integrated use of ruminants in farming systems that we consider the importance of crop residues in North Africa and West Asia. CROP RESIDUES FOR LIVESTOCK A basic problem in the study of national or regional feed trends is the lack of reliable data on feed use (Sarma, 1986, p. 51). This is particularly true of most crop residues and of grains which are fed on the farms where they are grown and never enter the market. Because they are mobile and a key store of wealth for farmers in this region, livestock are notoriously difficult to count with confidence. These facts mean one must make a number of assumptions about the national aggregations of livestock numbers , and national aggregations of diverse classes of crop residues, in order to present a simple picture of the use of these feed resources. This section of the paper is devoted to those assumptions . A simple picture is necessarily abstract and incomplete: in this case, the list of omissions may be longer than that of inclusions. To begin with, only 15 countries of the region have been selected for discussion: Afghanistan, Algeria, Egypt, Ethiopia, Iran, Iraq, Jordan, Libya, Morocco, Pakistan, Saudi Arabia, Sudan, Syria, Tunisia and Turkey; these were arbitrarily chosen 48 by the author only to illustrate some of the general tendencies. Only sheep, goats and cattle have been selected for review in this paper. Inevitably this has resulted in missing some important classes of livestock (e.g. buffaloes in Egypt and Pakistan, camels in Sudan etc), but these three classes are found in large numbers in all 15 countries and offer grounds for rough comparisons. Data on livestock numbers, by country for 1965 and 1985, were taken from the FAO Production Yearbook. An arbitrary weighting scheme was used to aggregate "animal units" in each country: one "animal unit" equals one cow or five sheep or five goats. The result (Appendix 1) is a very gross indicator of comparable "animal units" for each country in 1965 and 1985. The crops producing "residues for livestock" are likewise numerous . Ten crops were chosen for discussion purposes- -wheat, barley, rice, maize, sorghum and millet (as one), sugar-cane, sugar beets, lentils, faba beans and cotton- -since these are the main sources in this region. What is wanted here is a gross indication of dry matter quantities of the various residues offered to livestock, not simply the total quantities produced. Beginning with the national crop statistics published in the FAO Production Yearbook series, a number of assumptions are needed in order to estimate the amounts of crop residues for livestock grazing and feeding. The assumed multiplication factors (applied in Appendix 2) , for the 10 classes of crop residues are explained below: 49 WHEAT: Beginning with a harvest index of 47 (grain is 47% of the above-ground biomass) , and considering burning, trampling, shattering and handling losses, it is assumed that only 0.8 kg of wheat straw and chaff is offered to livestock for each kilogram of wheat grain harvested. BARLEY: With a harvest index of 41, it is assumed that 1.2 kg of residue is offered to livestock for each kilogram of barley grain harvested. This allows for some field losses but considers that barley straw is more fully used than wheat straw, partly because barley is grown in drier areas where feed is in shorter supply relative to livestock numbers. RICE: Rice has a similar harvest index to barley, but lower feed value than barley straw (much rice straw is used for bedding, fuel and paper manufacture). It is assumed that only 0.6 kg of rice straw and chaff is fed for each kilogram of rice grain harvested. MAIZE: Leaf stripping for fodder and use of the best parts of harvest residues by livestock amount, it is assumed, to only 2 kg of dry matter for each kilogram of maize grain harvested. The tough lower stalks are used for fuel. SORGHUM AND MILLET: The ratios of grain to total above-ground biomass are taken to be about 1 to 6 for both crops . Given that the poorer part of the stover is used for fuel, the dry-weight ratio of residues fed to grain harvested is assumed to be only 3 to 1 . SUGAR-CANE: It is assumed that only one kilogram of sugar-cane residue dry matter (stripped leaves and bagasse) is offered to livestock for every 10 50 kg of raw cane harvested. This considers that about 60% of the bagasse is used for fuel in the sugar mills (Ensminger and Olentine, 1978). SUGAR-BEET: The tops are normally grazed by live stock after the beets are harvested, amounting to about 30 g dry-weight for every kilogram of raw beets. About 1 kg DM of beet pulp goes to live stock feeding for every 15 kg of raw sugar-beet harvested. Therefore, total dry-weight residues for livestock feed (tops and pulps) are assumed to amount to only 0.1 kg for each kilogram of raw beet harvested. LENTIL: Lentil crops are characterised by harvest indices which increase with increasing seed yield; and in this region great care is taken in hand harvest of the crop to preserve the residues for livestock feed (Nordblom and Halimeh, 1982). For the sake of simplicity, however, it is assumed that 1 kg of lentil crop residue is available to livestock for each kilogram of seed harvested. FABA BEANS: The residues of this crop are used for feed and fuel in this region (Salkini et al , 1982). Allowing that the tougher stem parts go for fuel, it is assumed the amount of faba bean leaf and stem dry matter used as feed equals the weight of seed harvested for human consumption. COTTON: In this region, cotton seed and the leaves of cotton plants are important livestock feeds, and the woody stalks are used for fuel. It is assumed that the dry weight of leaves grazed, plus the amount of seed material fed to livestock, amount to 2 kg for each kilogram of cotton seed harvested. 51 Using these weighting factors, estimated amounts of "crop residues for livestock" were derived from the FAO data for each crop, for both 1965 and 1985; these are given in Appendix 2 as a service to those who do not agree with my weighting scheme. As is also the case in Appendix 1, readers can find the original FAO estimates and make their own "corrected" aggregations. AGGREGATE LIVESTOCK AND RESIDUES The results of these gross aggregations of "animal units" (in millions of head) and of "10 crop residues for livestock" (in millions of tonnes) are given in Figure 1 and Table 1. Use of the arbitrary multipliers in deriving these results reduces any discussion of significant digits to a simple warning: anything beyond the first digit cannot be trusted. This is not a great worry for the present purpose since we find differences, in some cases, of two orders of magnitude between countries, and large shifts over time within countries: it was most convenient to plot these values on log scales. One satisfying point in presenting such estimates is that all readers will be pleased in some way: those who are well informed on the crop- livestock relations in any of these countries will be pleased to attack my figures on solid grounds (1) of omitted classes of livestock and crop residues, (2) of the arbitrary weighting used in the aggregations, and (3) the inherent limitations of the data sources ; these people and others may be pleased with the similarities found, across large and small agricultural sectors, in the indicated relations between livestock and crop residues for livestock. 52 Figure 1 . Sheep, goat and cattle "animal units" and crop residuesfor livestock in selected countries ofNorth Africa and West Asia, 1965 and 1985. o 0> in o o tn> hi eno o in •- ♦+♦♦• =°* O NDF • Cellulose a Hemicellulose ♦ Lignin -40 -20 0 20 40 60 80 Days from anthesis Source: J. A. Lee (unpublished data). 208 indicating that a single regression from the pooled data, as is represented in whole straw, would be associated with wide variation and a lower r . Thus, the association of lignin with cellulose and hemicellulose is different in the three plant fractions and this must be taken into account. Few attempts have been made to alter lignin synthesis in growing plants. However, at the University of Melbourne, treatment of annual rye grass (Lolium rigidum) with gibberellic acid caused stem elongation and increased the propor tion of lignin in the cell wall. The SI contained 13% lignin in the NDF of the straw compared with 8% in untreated plants and the NDFD values were 17 and 26%, respectively. On the other hand, acute copper deficiency reduces lignin synthesis (Graham, 1976; Downes and Turner, 1986). The relationship between cell-wall composi tion and digestibility deserves a continuing high research priority. CELL CONTENTS The cell contents comprise proteins, peptides and other nitrogen-containing compounds, carbohy drates, fats and minerals. These are removed effectively from plant tissues by neutral - detergent solution, except for starch which often requires further digestion with amylase for complete removal. In senescing plants, fluctuations in NDS content are due mainly to changes in the amount of storage carbohydrates (fructans in wheat and starches in rice) . The levels of storage carbohy 209 drates retained in straw are critical to feeding value because of their high digestibility. The effects of changes in NDS in a senescing and dead internode of wheat on the digestibility of the internode are shown in Figures 6 and 7 . NDS increased rapidly from shortly before anthesis and peaked about 4 weeks after anthesis (Figure 6) . NDS digestibility was high throughout this period (Figure 7) , as would be expected of a tissue enriched with soluble carbohydrates. Subsequent ly, the amount of NDS in the internode and NDS and organic/dry-matter digestibilities declined. Both the amount of NDS and its digestibility approached basal levels at the time of grain maturation. The changes in the amount of NDS are associ ated with grain development in the following manner: Immediately after anthesis, photosyn- thates are produced in excess of requirements for grain growth because grain development is very slow. Grain mass increases rapidly from about 3 weeks after anthesis, consuming carbohydrates generated by current photosynthesis and, increas ingly, from the mobilisation of storage carbohy drates in the culm (Blacklow et al, 1984). The contribution that reserve carbohydrates make to the final grain mass depends upon environmental conditions and perhaps upon genetic factors. If the plant is stressed the reserves will be drawn upon heavily by the grain. For example, in drought-stressed barley Gallagher et al (1975) found that 74% of the grain mass could be attrib uted to storage carbohydrates, whereas other reports (e.g. Evans and Wardlaw, 1976) have suggested as little as 10%. The extent to which, and the conditions under which, storage carbohydrates are respired are uncertain. Rawson and Evans (1971) estimated that 210 Figure 6. Changes in mass ofdry matter and neutral-detergent solubles in S2 of wheat. Weight (mg) anthesis grain maturity grain harvest 400 300 200 - 100 O DM • NOS -40 -20 800 20 40 60 Days from anthesis Source: G.R. Pearce (unpublished data). Figure 7. Changes in IVOMD and NDS digestibility in S2 of wheat. Digestibility (%) anthesis grain maturity grain harvest 100 80 - 60 - 40 - 20 - O NDSD • IVOMD 0 20 40 60 Days from anthesis Source: G.R. Pearce (unpublished data). 211 30% of the fructans of wheat are used for respira tion, but L.C. Incoll (personal communication) found that almost all C -labelled fructans in stems are mobilised to the grains, indicating that, at least during grain filling, fructans are most probably not used for respiration. Another possible loss is transport to the lower parts of the plant to support late tillering. In certain crops and particularly under conditions of high fertility and moisture (e.g. irrigation), late tillering can occur. In rice this is called "rattooning" and is sometimes used as a means of obtaining a second grain harvest. NDS exhibits two main levels of digestibili ty; 90% when the stems are high in NDS and 40-50% when the stems are low in NDS , after they have senesced. It thus seems reasonable to consider NDS as being comprised of two pools of nutrients: (a) the intrinsic nitrogen compounds, carbohy drates, fats and minerals of the cytoplasm, mitochondria, membranes, nucleus, chloroplasts and other organelles, which, as a whole, are apparent ly less digestible in senescing and dead plant tissues, and (b) the reserve carbohydrates and proteins. Proteins are efficiently mobilised from senescing plant tissues and, except under condi tions of high nitrogen fertilizer application (e.g. Roxas et al, 1985), their concentration in straw is low (Dalling, 1985). However, consider able amounts of storage carbohydrates, such as fructans in temperate grasses (Ojima and Isawa, 1968) and glucans and starches in rice, may be present in dead crop dry matter. Different plant fractions do not store carbo hydrates uniformly. Stems store considerably more than leaf sheaths , which store more than leaf blades. In wheat, the penultimate internode, S2, 212 accumulates most fructans. In wheat, the upper parts of the culm contain larger proportions of NDS than the lower parts , as might be expected from their age, degree of senescence and proximity to photosynthesising leaves in the crop canopy. In irrigated rice , however , there may be no difference in the NDS content of the upper and lower parts of the straw (Hart and Wanapat, 1985; Winugroho, 1986). The proportion of NDS in wheat straw ranges from 12% (W.J. Wales, unpublished data) to 41% (Ayres et al, 1976) of the dry matter and in rice straw from 14% (Cheva-Isarakul and Cheva-Isarakul , 1984) to 46% (Roxas et al, 1984). Higher values are associated with higher digestibility because of greater amounts of residual storage carbohy drates. In considerations of straw quality, therefore, the role of the storage carbohydrates is critical: the more storage carbohydrates remaining in straw the higher the digestibility. This has been expressed by Pearce (1984) as a high correlation between NDS% and IVOMD% . The perti nent question, therefore, is under what conditions are residual storage carbohydrate levels high in straw? The answer lies in the interactions between the photosynthetic activity of the plant at critical time periods and the demands of the grain. The first requirement for high levels of storage carbohydrates is a high level of accumula tion during the period around anthesis and for some time afterwards . For wheat in southern Australia this period spans about 40 days, from about 10 days before anthesis to about 30 days afterwards. Storage carbohydrates accumulate during this period if conditions are favourable for photosynthesis, i.e. suitable light and 213 temperature conditions, adequate nutrient and water availability and the absence of disease. Thus, the history of the plant in terms of soil fertility, fertilizer application, spacing of plants and leaf development up to this time may be important . The full extent to which storage carbohydrate accumulation varies is not known but, under a range of conditions at the University of Melbourne, amounts of NDS in stem segments varied widely. For example, among five different, but related, wheat cultivars grown side-by-side in the same season, NDS content of the S2 at peak accumu lation ranged from 114 to 280 mg. The NDS content of S2 of plants grown under normal field condi tions peaked at 158 mg, compared with only 60 mg for the same cultivar grown under apparently favourable conditions in pots in a glasshouse (W.J. Wales, unpublished data). Ambient tempera tures and rates of growth relative to crop photo - synthetic activity may all have an effect on the accumulation of carbohydrate reserves. Under field conditions in Western Australia, M. Nicolas (personal communication) has concluded that wheat cultivars do, however, vary widely in their ability to accumulate fructan reserves . The second requirement for high levels of storage carbohydrates in straw is a low rate of removal. Normally, developing grains draw on storage carbohydrates to augment the metabolites provided by current photosynthesis. As current photosynthesis declines during senescence the reserves are drawn upon. If current photosynthe sis is optimal then the extent to which reserves are used depends largely on the number of grains developing, i.e. the size of the "sink". If there are few grains levels of storage carbohydrates and 214 straw quality are more likely to be high. How ever, correlation between grain yield and straw quality is often poor (e.g. Erickson et al , 1982), partly because of the variable accumulation and loss of storage carbohydrates. Where the sink is small, mobilisation of storage carbohydrates may be delayed and reduced if sufficient moisture and nutrients are available for the crop. This may happen under irrigation but in dryland situations seasonal constraints are likely to predominate. At this stage, it is only possible to con clude that the relationships between the amounts of residual storage carbohydrate in straw and other physiological events involved in yield formation in crops are likely to be complex. However, an understanding of these interactions may identify opportunities for manipulation of carbohydrate reserves so as to achieve high- quality straw for animal production without significant reductions in grain yield and quality. ANIMAL FACTORS INTERACTING DIRECTLY WITH STRAW CHARACTERISTICS Straw intake and digestibility in ruminants are influenced by straw characteristics (including chemical composition, morphological and anatomical features, physical nature and palatability) ; by feeding conditions (including the amount offered and the frequency of feeding) ; and by animal char acteristics (including species/genotype, live- weight, age, body condition, type and level of production and disease) . Extremes of temperature and humidity and social interactions between animals may also affect intake. Reviews on 215 herbage digestibility (e.g. Akin, 1982) and intake (e.g. Armstrong, 1982) have discussed the princi ples involved, but without specific reference to straws. A major limitation is the small number of experiments in which animals have been fed straw alone; the diet has usually been supplemented with nitrogen and minerals and, often, energy. The following discussion is limited to specific aspects that are particularly relevant to straws. Selection in relation to physical characteristics of straws Weston (1985) included texture as a criterion governing acceptability of feeds and Hogan et al (1986) suggested that animals select plant mate rial on the basis of "tenderness." However, such characteristics are difficult to assess because, often, no one feature predominates and several factors interact. In straws, such as wheat (Doyle et al, 1987) and barley (Wahed and Owen, 1986) animals usually show a preference for leaves rather than stems. Where such preference is shown, useful comparisons between many literature reports are almost impossible because of the lack of information on feeding procedures and because of unspecified degrees of selection, especially when straws have been offered in excess of appetite. In rice straw, selection of leaves in preference to stems may not occur (Doyle et al , 1987) , possibly because the leaf blades contain more silica than the stems (Doyle et al, in press) , as suggested by Van Soest (1982) . 216 Resistance to particle size reduction If the plant material is highly resistant to particle size reduction voluntary intake will be reduced because large particles of digesta cannot pass through the reticulo-omasal orifice into the lower digestive tract. Thus, large particles are retained in the reticulo- rumen until they are broken down by rumination or detrition. The comminution of feed particles during chewing also contributes to this process. Lee and Pearce (1984) found that, in five roughages, including barley and oat straw, chewing by cattle reduced about 50% of the material to particles that would pass through a 1 mm screen. The extent and rate of particle size reduc tion is not the only mechanism controlling rough age intake and the rate at which digesta leave the reticulo -rumen is not necessarily proportional to feed intake because (a) the amount of digesta in the reticulo -rumen can vary and (b) the rate and extent of fermentation varies according to the available nutrient content of the roughage. Thus, straws of differing composition would be expected to produce differences in fermentation kinetics. However, the full details of the system have not been resolved. Grinding energy has been used as an index of resistance to particle size reduction. This is the amount of electrical energy required to grind 10 g of feed through a 1 mm screen (Chenost, 1966; Foot and Reed, 1981). In wheat straws, the grinding energy of leaf blades is lower than that of leaf sheaths which is lower than that of stems , but in rice straw the differences may not be as great (Table 8) . In experiments with wheat straw (W.J. Wales, unpublished data) and with rice 217 Table 8. Grinding energy (J g DM) of wheat and rice straw fractions (averages from three straws) . Fraction Wheat straw Rice straw Leaf blade 83 100 Leaf sheath 122 103 Stem 213 147 Segments were chopped into 2 cm lengths prior to grinding. Source: Doyle et al (in press). straws (Chanpongsang, 1987), good inverse rela tionships were obtained between intake by sheep and grinding energy within cereal species but not between species (Table 9). Other factors, including possibly silica content, are thus involved. Table 9 . Intake , grinding energy and rate of eating for three wheat and three rice straws . Wheat straw Rice straw Measurement Intake (g OM d"1) 617 484 303 492 383 369 Grinding energy (J g"T DM) 138 161 195 95 109 107 Rate of eating (g air dry h"1) 516 434 287 386 309 269 Sources: W.J. Wales (unpublished data); Chanpongsang (1987) . 218 Eating rate Eating rate has been used to evaluate herbage quality. Table 9 shows positive relationships between intake and eating rate of wheat and rice straws. These measurements were made with trained sheep and reflected characteristics of the feeds associated with palatability or acceptability. With wheat straw, material with a high proportion of stem is eaten much more slowly than leafy material. Habituation is also a factor, because straws that are eaten relatively slowly in early tests may be eaten more quickly in later tests. This occurred particularly with rice straws in which, it is believed, silica levels may have affected acceptability initially. The specific plant causes of such animal responses are unknown. Metabolic factors influencing intake of straws Voluntary intake of highly digestible forages is controlled by metabolic factors or is linked to requirements for maintenance and production. In the case of poorly digestible materials, however, attention has been focused on physical control of intake, particularly distension of, and removal from, the reticulo- rumen. However, the amounts and balance of nutrients supplied by low- quality straws are so limiting that metabolic contribu tions to the control of intake should not be overlooked. Doyle et al (1987) concluded that, in view of the relatively small amount of digesta in the reticulo -rumen of animals fed unsupplemented straws, the purely physical control mechanisms do not operate or the levels at which the system is 219 sensitised are lower, due perhaps to nutrient imbalances in the tissues. In either case, an extremely complex set of interactions determines intake levels. The kinetic features of digestion for straws with varying proportions of nutrients and for straws which are supplemented to provide limiting nutrients are variable. CONCLUSIONS In this paper, attention has been directed towards the characteristics of the cell wall and cell contents as they determine the nutritive value of cereal straws, and reference has been made to some other factors directly affecting intake and diges tion of straws by animals. Because of differences between morphological fractions of plants, only limited information can be obtained from assess ments of whole straws. Different harvesting, threshing and feeding practices , which affect the proportions of the main morphological fractions, will determine the nutritive value of the straw actually consumed by animals . Cell -wall digestibility can be improved by chemical and other treatments but such procedures are too expensive for wide practical application. The alternatve, separating material with high digestibility (e.g. leaf blades in wheat) from material with low digestibility (e.g. stems in wheat) , is also expensive and suffers from the disadvantage that the less digestible fraction usually forms the largest proportion of a crop residue. Breeding for greater leafiness may also not be attractive because this would lower the harvest index. 220 The main factor determining the digestibility of cell-wall material is lignin, but the precise limiting role of lignin is still unresolved. The information presented in this paper indicates that lignification effects need to be studied in dis crete plant tissues. Identification of periods during which cell -wall digestibility is changing rapidly probably provides the best opportunity to understand the significance of concurrent chemical changes. The thrust of agronomic or genetic manipulations to alter cell wall characteristics must await a clearer understanding of lignin chemistry in relation to other cell wall constituents . The potential contribution of the cell contents to the nutritive value of straws appears to have been under-estimated in the literature. Not only can straws contain quite large propor tions of cell contents, but the amount of storage carbohydrates in the cell contents can vary widely. Because storage carbohydrates are highly digestible (probably 100%) , they may have a marked effect on the nutritive value of straws. In this paper, the pattern of accumulation and subsequent removal of solubles in wheat stem internodes has illustrated the means by which varying amounts of storage carbohydrates remain in straws. However, the precise mechanisms involved have not been elucidated. Complex interactions occur between storage carbohydrate metabolism and other physio logical processes in the plant, mediated by envi ronmental and genetic factors. Only an under standing of these will permit genetic improvement of straw quality without reducing grain yield and quality. Factors in straws that impinge directly upon an animal's senses, thus influencing its level of 221 intake, have not been studied in detail, partly because straws have rarely been fed without supplementation. It is clear, however, from the available results that important differences may occur. To date, these have been monitored as differences in features such as grinding energy, eating rate and chemical composition, but alone or collectively they may result in pronounced differ ences in voluntary intake by animals, often asso ciated with high degrees of selection for certain plant parts. The precise plant features that are responsible and the variation between animals in response to these have not been defined. Again, an understanding of these is necessary so that appropriate manipulations , by genetic or other means, may be approached. ACKNOWLEDGEMENTS Much of the research conducted in this area at the University of Melbourne was funded by the Austra lian Wool Corporation through the Wool Research Trust Fund, the Australian Meat and Livestock Research and Development Corporation, the Austra lian Centre for International Agricultural Research and The University of Melbourne. REFERENCES Acock C W, Ward J K, Rush I G and Klopfenstein T J. 1978. Effect of location, variety and maturity on characteristics of wheat straw. Journal of Animal Science 47 : Supplement 1:327 (Abstract) . Akin D E. 1982. Microbial breakdown of feed in the digestive tract. In: J B Hacker (ed.), Nutritional limits to animal production from 222 pastures . 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Blacklow W M, Darbyshire B and Pheloung P. 1984. Fructans polymerised and depolymerised in the internodes of winter wheat as grain- filling progressed. Plant Science Letters 36:213- 218. Braman W L and Abe R K. 1977 . Laboratory and in vivo evaluation of the nutritive value of NaOH- treated wheat straw. Journal of Animal Science 45:496-505. Chanpongsang S. 1987. Variation in the nutritive value of rice straws. M.Agr.S. thesis, University of Melbourne, Australia. Chenost M. 1966. Fibrousness of forages: Its determination and its relation to feeding value. In: Proceedings of the Tenth 223 International Grassland Congress , held in Helsinki, Finland, 7-16 July 1966. Valtioneuvoston Kirjapaino, Helsinki, Finland. Cheva-Isarakul Boonlom and Cheva-Isarakul Boonserm. 1984. Comparison of the intake and digestibility of different crop residues by sheep, cattle and buffaloes. In: P T Doyle (ed.), The utilizatation of fibrous agricultural residues as animal feeds. 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Animal Production 42:89-95. Weston R H. 1985. The regulation of feed intake in herbage -fed ruminants. Proceedings of the Nutrition Society of Australia 10: 55-62. White L M, Hartman G P and Bergman J W. 1981. In vitro digestibility, crude protein, and phosphorus content of straw of winter wheat, spring wheat, barley, and oat cultivars in eastern Montana. Agronomy Journal 73:117- 121. Winugroho M. 1981. Studies on the utilization of cereal straws. M.Agr.S. thesis, University of Melbourne, Australia. Winugroho M. 1986. Intake and digestibility of the upper and lower fractions of rice straw by sheep and goats. In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1985. Proceedings of the Fifth Workshop of the AAFARR Network held in Bogo, Indonesia, 13-17 April 1985. Inter national Development Program of Australian Universities and Colleges, Canberra, Australia. Yoon C S, Choi E S, Oh T K, Lee N H, Kim C W and Kim C S. 1982. Effects of aqueous ammonia- treated rice straw on feed intake, nutritive value and rumen characteristics. Korean Journal of Animal Science 25:613-622. Yu Yu, Thomas J W and Emery R S. 1975. Estimated nutritive value of treated forages for ruminants. Journal of Animal Science 41:1742-1751. 229 DISCUSSION Van Soest: I am pleased to see the relationship between the cell walls and the lignin. How did you measure the digestibility of the neutral -detergent solubles and what is the indigestible fraction? Pearce: We measured neutral -detergent solubles as 100% minus the neutral -detergent fibre. We measure the NDF before we start and the NDF of the residue and 100-NDF is the indigestible neutral detergent solubles . Van Soest: Is this after cellulase digestion? Pearce: Yes, after pepsin-cellulase . Van Soest: There might be fractions in there that might be digestible by other enzymes . Is that possible? Pearce : Such as what? Van Soest: Such as pectins, galactans, soluble hemicelluloses or phenolics. Pearce: There is not much pectin in wheat straw. How else can we measure the digestibility of neutral -detergent solubles? Van Soest: The Lucas test on straw indicates that the neutral-detergent solubles have a 90% plus true digestibility and wheat straw follows that relationship in animal digestion trials. Pearce: Yes, although I am not convinced about that. It is quite plausible that, in the absence of soluble carbohydrates , the cell contents are not completely digestible. Chloroplasts are probably undigestible and membranous materials and nucleus residues are only 20% digestible . 230 Uden:- I think the difference between the animal work and the cellulase work is that you can never tell the digest ibility of the neutral -detergent solubles in vivo. A lot of soluble compounds are excreted in the urine. Chesson has found low digestibility of chloroplasts and other organelles in the cell solubles. Pearce : Yes, it0s impossible to get an estimate of digestibility of neutral- detergent solubles because of all the material that is added on the way through the digestive tract. Thomson: You made the comment that you should try to have more cell contents in the straw. How will that affect grain yield? Pearce: Under favourable conditions the grain does not rely very much on the stored fructans in wheat. I am not suggesting that we need to retain all the fructans, why not use enough for the grain and save the rest? We need to reduce wastage by respiration in the senescing plant. On the other hand, if the plant is stressed during grain development, it might be detrimental . 231 FACTORS AFFECTING THE NUTRITIVE VALUE OF SORGHUM AND MILLET CROP RESIDUES 12 3Jess D. Reed , Yilma Kebede and Les K. Fussell 1. ILCA, P.O. Box 5689, Addis Ababa, Ethiopia 2. Institute of Agricultural Research, Nazareth, Ethiopia. 3. International Crops Research Institute for the Semi-Arid Tropics, Sahelian Center, B.P. 12404, Niamey, Niger INTRODUCTION Sorghum (Sorghum bicolor) and pearl millet (Pennisetum typhoides) are the most important food crops in the semi-arid, drought-prone areas of Africa. Over 10 million tonnes of grain from each cereal are produced annually, 95% of which is used for human food (Hulse et al ,0 1980). Sorghum and millet crop residues are an important potential feed resource. In 1981, 55.2 and 51.4 million tonnes of crop residue were produced from sorghum and millet respectively (Kossila, 1985) . Assuming a digestibility of 45% and 20% wastage, the annual maintenance require ments of 39 million tropical livestock units (250 kg liveweight) could be met by sorghum and millet crop residues supplemented with low- levels of protein or non-protein nitrogen. However, to raise productivity above maintenance, digestibili ty and protein supplementation would need to be increased. Livestock are an important component of agricultural systems in the semi-arid regions of Africa. They are an important source of income 233 and a means of saving capital for use in times of need. Under conditions of improved productivity, livestock may serve as a catalyst to increase overall farm productivity. Ruminant livestock can complement crop production by increasing soil fertility through manure, by providing traction for cultivation, by grazing areas that can not be cultivated and by using crop residues for feed. However, poor nutrition is a major constraint to increased livestock productivity. Feed is often in short supply and nutritive value low. Grazing and crop residues are low in protein and energy and may also be deficient in important mineral nutrients. Improved livestock feeding systems need to be developed for the smallholder farmer of Africa who depends on millet and sorghum for subsistence. Although these cereals are a staple food crop, they have low economic value during years of average and above average rainfall. The stability and overall productivity of farming systems could be improved by the introduction of livestock rearing activities that combine efficient use of crop residues with forage legumes and multi purpose trees . Although much research has been devoted to upgrading straw by chemical treatment (Jackson, 1978) , little attention has been given to varia tion in the nutritive value of untreated crop residues as influenced by variety and environment. Quantity and quality of cereal crop residues are important criteria in a farmer's decision to grow a particular variety. Varietal and environmental effects on the nutritive value of cereal crop residues are also important. The nutritive value of residues from a given variety varies widely due to differences in growing conditions (season, 234 elevation or latitude) . High temperature during growth increases cell wall and lignin contents and decreases digestibility (Deinum, 1976). High humidity and rain during and after grain harvest reduce nutritive value. Loss of leaves through wind or trampling of cereal crop residues left in the field also causes deterioration. These losses can be reduced by improved conservation practices. It is well known that cereal crop residues are deficient in protein. However, supplementa tion with non-protein nitrogen or protein does not always increase intake and digestibility because other factors limit nutritive value. These factors need to be determined because, within the range of energy intake of cereal crop residues, large increases in animal productivity can be achieved by relatively small increases in digestibility and intake. Cell wall, as estimated by neutral -detergent fibre , accounts for as much as 80% of the dry matter in cereal crop residues and represents a large source of energy for ruminants. However, the ability of rumen micro-organisms to digest cell wall polysaccharides (cellulose and hemicel- lulose) is limited by the presence of phenolic and other aromatic compounds which are generally referred to as lignin. The phenolic constituents of sorghum and millet have been subject to little investigation. However, the digestibility of the crop residues will be correlated with the nature and amount of phenolics associated with their cell walls and the influence of environment on phenolics (Hartley, 1981). 235 SORGHUM In Africa, birds are a major crop pest and limit grain production from sorghum (Bullard and Elias , 1980) . Bird resistance is related to the amount of proanthocyanidins (condensed tannins) in the grain (Gupta and Haslam, 1980) . Sorghum improve ment programmes in Africa are breeding for bird resistance in varieties for semi-arid zones. The phenolic content of the vegetative components of bird resistant (BR) and forage varieties is negatively associated with digestibility (Saini et al, 1977; Cummins, 1971). Weanling rats fed a diet containing leaves from BR varieties had lower feed efficiency and N retention than those fed a diet containing leaves from non-bird-resistant (NBR) varieties (Gourlay, 1979). In this section the differences between BR and NBR varieties in content of phenolics and their relationship to digestibility of fibre in the crop residue are discussed. BR and NBR varieties do not differ in their N or neutral -detergent fibre (NDF) contents and leaves contain twice as much N as stems (Reed et al, 1987). The total cell wall as estimated by NDF is greater than 70% of the organic matter in sorghum leaves. Silica is also a cell wall component (Jones and Handreck, 1967), but is not completely recovered in the NDF. Silica content of sorghum leaves (9 to 15% of the dry matter) is much higher than that found in temperate forages and most other cereal crop residues (Reed et al , 1987). Most of the energy obtained by ruminants fed sorghum crop residues comes from rumen fermenta tion of cell wall carbohydrates. Factors that limit the digestibility of these carbohydrates 236 would have the greatest influence on differences in nutritive value between varieties after N deficiencies are corrected. Leaf blades and leaf sheaths from BR varieties have higher levels of insoluble proanthocyanidins and soluble red pigments than those of NBR varieties (Table 1) . Leaf sheaths from BR varieties are higher in lignin than those from NBR varieties. In leaves and stems, linear correlation coefficients among insoluble proanthocyanidins, soluble red pigments and soluble phenolics as measured by absorbance are positive and significant (Table 2) . Leaves and stems from BR varieties contain red pigments that are extracted by polar organic solvents. However, NDF from BR varieties, prepared by sequential extraction with aqueous acetone and neutral - detergent , is also red. Red pigmentation, as measured by absorbance of insolu ble proanthocyanidins at 550 nm, is associated with larger amounts of lignin in BR varieties (Figure 1) . In leaves, lignin, insoluble proanthocyani dins and soluble red pigments contents are nega tively correlated with extent of NDF digestion and digestibility of NDF at 48 hours, and positively correlated with indigestible NDF (Table 3) . Insoluble proanthocyanidins and soluble red pigments contents are negatively correlated with rate of NDF digestion. Phenolics are a major factor limiting digest ibility of NDF in leaves. BR varieties are higher in phenolics than NBR varieties. Digestibility of NDF at 48 hours is an important parameter because it is used to estimate in vivo digestibility 237 •0N0"7=v0"700"7= 0Uu4otjtuSts:> u Nn aou«oTj •jsisa^ 0 0 0 000 0 00 * 0 000 000 0* 0 0 - V0'f Tu8tN "TN 00 00 0 000 0 0 000 000 000 000 000 00 0 - 000 0N 0 00 $■30 T'V0 0L Z00 aiqsQ 0 •30 Zst 00 80 00 0Z 80 60 00-0 T00 0L 00 •3'T 00 «a UB3H 0Z9 T'Z0 00 800 V00 0'6L 0T0 09 0T0 000 0Zi. 6Z0 89 000 sapB0[qJE30 (wox)&Nn (x)jNNN (WOX)UTU80IT 'T°s0NV ■■[osut0NV (WOX)Ann sl[^bbi[SJVBNl (X)i0NO (WOX)"T"8t0 ■■[OS0NV Tosut0NV (WOX)MM (X)iON0 (W07.)"TuSti ■[os0NV ■0[osu0f0NV SIU33N ■S3158IJEAumn0aos(8=u'0N)au4jSTSsj-pj-iq -uousu4(9='ag)j 4jsTssjP^Tq3°snp S"s aoat\iuiojuj ^s4sqirq jr'T'S3ppr0[q4a0[ui(-0[osu0t0NV)suTp00>4Xooqiu4ojsm[ i0[ suiu4■0NV) siU3ui90tsp3Ja0[ui0[os'u0i 8f7jojtlajuoo'(J N0)i N°^3TTTqT3 a8TpNN)3JqTJU33J333P[53011 41°U33UOOSOUB^SISSJP^ q"«HTOD J.I'^ ! 00m CSI Table 2. Linear correlation coefficients among lignin, insoluble proanthocyanidins , soluble red pigments and soluble phenolics as measured by absorbance at 280 ran (A280) in leaves and stems from 24 sorghum varieties . Insoluble proantho- Lignin cyanidins Soluble red pigments Leaves Insoluble proanthocyanidins 0.733** Soluble red pigments 0.762** Soluble phenolics 0.446* 0.917** 0.457* 0.599** Stems Insoluble proanthocyanidins 0,.286 Soluble red pigments 0.,390 0.826** Soluble phenolics 0.,401 0.726* 0.909** Source: Reed et al (1987) * P<0.05. ** P<0 . 01 . (Goering and Van Soest, 1970). Phenolics (lignin and insoluble proanthocyanidins) accounted for most of the variation in digestibility of NDF at 48 hours in leaves (Figure 2). Environmental factors have a large effect on pigmentation in sorghum leaf blades and sheaths. BR varieties grown at Melkasa (elevation 1500 m) 239 Figure 1 . Relationship between lignin and insoluble proanthocyanidins con tents of leaves from the crop residue of bird-resistant and non-bird- resistant sorghum. O m in < o ki a. 0) _5 o u> c 0.18 - 0 = Bird resistant 0 X = Non bird- resi stant 0 0. 16- Y = 0.056x-0.24 r=0.733 P<0.0l 0 0.14- 0 0 0.12- 0 °0 0 0. 10- oy^ 0.08- 0 0 0 0.06- X y^ 0 0.04- X y /^ X X X X X 1 T 1 I I 1 —1— i r 1 1 4.6 5.0 5.4 5.8 6.2 Lignin (% 0M ) 6.6 7.0 in the Ethiopian Rift Valley had greater pigmenta tion in blades and sheaths than the same varieties grown at Debre Zeit at higher elevation (1800 m) . The effects of these phenolic pigments on NDF digestibility was greatest in leaf sheaths from BR varieties grown at Melkasa (Table 1) . Average maximum temperatures during the growing season at Melkasa were 2 to 3° C higher, and average minimum temperatures 5 to 7°C higher, than at Debre Zeit. Total rainfall during the growing season was 645 mm at Melkasa and 693 mm at Debre Zeit. The mean digestibility of leaf sheaths from BR varieties grown at Melkasa was 8.4 percentage units lower than that of the same varieties grown at Debre Zeit and over 12 units lower than that of NBR varieties grown at either site (Table 1) . These 240 Table 3. Linear correlation coefficients between parameters of digestibility of neutral - detergent fibre (NDF) and lignin, insoluble proanthocyanidins , soluble red pigments and soluble pbenolics as measured by absorbance at 280 nm in leaves and stems from 24 sorghum varieties . Potentially Rate Indigest- NDF digestible of NDF ible digestion NDF digestion NDF at 48 h Leaves Lignin Insoluble proantho cyanidins -0.525** Soluble red pigments -0.553** Soluble phenolics -0.542** 0.784** -0.248 0.808** -0.884** ■0.518* 0.520* -0.797** -0.493* 0.623** -0.846** -0.195 0.491* -0.603** Stems Lignin 0.270 Insoluble proantho cyanidins 0.390 Soluble red pigments 0.410 Soluble phenolics 0.362 * p<0.05. ** p<0 . 01 . -0.099 0.759** -0.364 0.222 0.067 0.361 0.295 0.214 0.366 0.247 0.270 0.249 241 Figure 2. Relationship between digestibility ofneutral-detergentfibre (DNDF) and lignin and insoluble proanthocyanidins in leaves from the crop residue ofbird-resistant and non-bird-resistant varieties ofsorghum. DNDF (%) 72 -| O Bird resistant 70 X X Non-bird-resistant 68 H 66 64- 62 - 60- 58 56 54-| 52 50 48 Y = -8.5X+I09 r = -0.884 P < 0.01 46 4.6 DNDF (%) 72 70- 68 - 66- 64- 62 60 58 56 54 52 50 48 5.0 5.4 5.8 6.2 Lignin (% OM) 6.6 7.0 46 Y = - 97.8 x+ 67.9 r =- 0.792 P< 0.01 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 Insoluble proanthocyanidins (A 550 ) 0.18 242 results suggest that phenolic pigments have their greatest effect on leaf sheath digestibility and that environmental effects may also be greatest on this plant fraction. In stems, there is a significant correlation between lignin content and indigestible NDF but no correlation between lignin content and digestibil ity of NDF at 48 hours (Table 3) . Lignin may be more unevenly distributed in stems than in leaf blade and sheaths. The amount of lignified tissue may determine the amount of indigestible NDF in relation to different proportions of rind and pith. Soluble red pigments and insoluble pro- anthocyanidins contents are lower in stem than in leaves, suggesting that these phenolics are less important in the digestion of NDF in stems (Reed et al, 1987). The range in NDF digestibility in leaves and stems from sorghum crop residue is large. The amount of phenolics in leaves accounts for most of the variation in digestibility. Leaves are more important than stems in determining nutritive value because of their greater N content and greater consumption by livestock (Powell, 1984). BR varieties have a higher phenolics content than NBR varieties. These relationships indicate that breeding for bird resistance in sorghum lower the nutritive value of the crop residue. However, some varieties may have bird-resistant grain and low phenolic content in the crop residue. Such varieties may be useful in farming systems in semi -arid areas of Africa where birds are an important pest and the crop residue is an important feed. Five sorghum varieties , selected on yield criteria, were used to determine the effect of 243 variety on intake and digestibility of the crop residue in mature highland zebu oxen. After grain harvest, the crop residue from each variety was coarsely chopped and fed to five oxen in a latin square design. Oxen were offered 12 kg of crop residue dry matter per day. This diet was supplemented with 60 g of urea added to the drinking water. Daily dry-matter intake varied by more than 1 kg among varieties (Table 4) . The variety with the lowest intake (MW5020) is a dwarf, bird- resistant variety which gives high grain yield but little residue. MW5020 had the highest proportion of leaves in the crop residue but its leaves were strongly pigmented. It was the only variety with a measurable amount of leaf in the feed refusals. The intake of digestible energy from MW5020 would be adequate for maintenance requirements only, whereas the intake from Melkamash and 5DX 160 would allow weight gains of over 200 g per day. Table 4 . The effect of sorghum variety on intake of crop residue by highland zebu oxen. Variety Mean intake Percent (kg day"1) leaves (n-5) 43.7 4.11a 23.2 4.43a 37.9 4.90b 39.3 4.96b 35.3 5.18b MW5020 Buraihi 2KX17 Melkamash 5DX-160 Means with different superscripts are significantly different (p < 0.05). 244 MILLET Variety had a significant effect on NDF content and NDF digestibility in blades, sheaths and stems from 12 millet varieties (Table 5) , and on lignin content in blades and stems. The millet varieties were sampled from an advanced agronomic trial at the ICRISAT (International Crops Research Institute for the Semi-Arid Tropics) Sahelian Center, Sodore , Niger. Table 5. The effect of variety on content of neutral -detergent fibre (NDF) , digestibility of NDF (DNDF) and content of lignin in leaf blades , leaf sheaths and stems from the crop residue of 12 millet varieties. Varietal Leaf blade Mean Range effect NDF (% OM) 59.9 57.7-63.0 /NwV DNDF (%) 60.1 55.7-62.2 *** Lignin (% OM) 3.9 3.5- 4.5 ** Leaf sheath NDF (% OM) 69.2 65.5-70.8 ** DNDF (%) 42.4 38.1-44.9 ■Jck-k Lignin (% OM) 5.1 4.8- 5.9 NS Stem NDF (% OM) 76.2 72.5-79.6 ■A-* DNDF (%) 30.7 27.6-35.2 "k Lignin (% OM) 8.7 7.6- 9.7 *** Varietal effect significant at: * P<0.05; ** P<0.01; *** P<0.001; NS not significant. 245 Although varietal effects were significant, the range in parameters of nutritive value among varieties is lower than among sorghum varieties . The range in NDF digestibility within sorghum plant parts is greater than 15 percentage units (Figure 2) , whereas in the 12 millet varieties tested the range was less than 8 percentage units (Table 5) . Millet lacks the phenolic pigments that have a large effect on NDF digestibility in BR sorghum varieties. The digestibility of NDF in the leaf sheath and stem fractions of the 12 millet varieties was low. Varieties with higher digestibility and adaptation to the Sahel need to be sought. CONCLUSIONS Crop residues will continue to be important feed resources in developing countries and increased ruminant production can be accomplished through improved utilisation of the crop residues from sorghum and millet. Dairy producers in many urban areas of India depend on these crop residues as the major source of roughage. They are supplied by smallholder farmers at organised fodder markets and sale of crop residue can account for more than 50% of total income from crops (Parthasarathy Rao, 1985) . These dairy enterprises are meeting the increased demand for milk and milk products in urban areas of India (Walker, 1987). Similar ruminant production systems exist around urban areas in Africa. More efficient utilisation of sorghum and millet crop residues could contribute to increased productivity and income for both livestock producers and small holder farmers . Crop improvement programmes could 246 improve these systems by developing crop varieties that are suitable for dual purpose production of both grain and fodder . REFERENCES Bullard R W and Elias D J. 1980. Sorghum polyphenolics and bird resistance. In: J H Hulse (ed.), Polyphenols in cereals and legumes. IDRC, Ottawa, Canada. Cummins D G. 1971. Relationships between tannin content and forage digestibility in sorghum. Agronomy Journal 63:501-502. Deinum B. 1976. Effect of age, leaf number and temperature on cell wall and digestibility of maize. In: Carbohydrate research In plants and animals . Miscellaneous Papers, Agricultural University, Wageningen, No. 12:29-41. Goering H K and Van Soest P J. 1970. Forage fibre analysis . Agriculture Handbook No. 379. Agricultural Research Service, United States Department of Agriculture, Washington DC, USA. Gourlay L M. 1979. Nutritional quality of sorghum leaves. In: Eleventh biennial grain sorghum research and utilisation conference , Lubbock, Texas, USA. Gupta R K and Haslam E. 1980. Vegetable tannins - structure and biosynthesis. In: J H Hulse (ed.), Polyphenols in cereals and legumes. IDRC, Ottawa, Canada. Hartley R D. 1981. Chemical composition, properties and processing of lignocellulosic wastes in relation to nutritional quality for animals. Agriculture and Environment 6:91- 113. 247 Hulse J H, Laing E M and Pearson 0 E. 1980. Sorghum and millets: Their composition and nutritive value. Academic Press, London, UK. Jackson M G. 1978. Treating straw for animal feeding. FAO Animal Production and Health Paper 10. Food and Agricultural Organization of the United Nations, Rome, Italy. Jones LHP and Handreck K A. 1967. Silica in soils, plants and animals. Advances in Agronomy 19:107-149. Kossila V S. 1985. Global review of the potential use of crop residues as animal feed. In: T R Preston, V L Kossila, J Goodwin and S B Reed (eds) , FAO Animal Production and Health Paper 50 . Food and Agricultural Organization of the United Nations, Rome, Italy. Parthasarathy Rao P. 1985. Marketing of fodder in rural and urban areas of India. In: Agricultural markets in the semi-arid tropics. Proceedings of the International Workshop, 24-28 October 1983, ICRISAT Center, Patancheru, India. International Crops Research Institute for the Semi -Arid Tropics, India. Powell J M. 1984. Sorghum and millet yields and consumption by livestock in the subhumid zone of Nigeria. Tropical Agriculture (Trinidad) 62:77-81. Reed J D, Tedla A and Kebede Y. 1987. Phenolics, fibre and fibre digestibility in the crop residue from bird resistant and non-bird resistant sorghum varieties. Journal of the Science of Food and Agriculture 39:113-121. Saini M L, Paroda R S and Goyal K C. 1977. Path analysis for quality characters in forage sorghum. Forage Research 3:131-136. Walker T S. 1987. Economic prospects for agroforestry interventions in India's SAT: Implications for research resource allocation 248 at ICRISAT. Resource Management Program, Economics Group, Progress Report- 79. International Crops Research Institute for the Semi-Arid Tropics, Patancheru, India. DISCUSSION Berhane : Reed: Berhane : Reed: What are the implications for a plant breeding programme when temperature has such a large effect on pigmentation and digestibility? We need to look for low pigmented, bird-resistant cultivars. Pigmentation varies considerably among bird-resistant cultivars but this is also heavily influenced by environment, which could lead to genotype by environment interactions. We could score blade pigmentation at various sites; this could easily be incorporated into bird-resistance trials . You singled out one variety which was bird resistant and was high in tannin and high in digestibility. Was that variety incorporated in animal feeding trials? I cannot recall if we used this variety in our feeding trials . The variety that had the highest intake in the oxen trial was selected because of the high digestibility of its stems, which indicates that stem digestibility may be a major factor determining the nutritive value of sorghum. This variety was also bird resistant. 249 prskov: What is the correlation between stem, blade and sheath digestibility? Reed: The correlation was very poor in our data on sorghum. Pearce : In ryegrass the correlation is quite good: if stem is highly digestible, the sheath and blade will also be highly digestible. Capper: We looked at botanical fractions in sorghum at ICRISAT. When you plot these against height, over the range of 150 to 300 cm there is little change in the proportion of botanical fractions , but below 150 cm the amount of leaf sheath, which is the least digestible fraction and in which there was the most variation in digestibility, starts to increase quite rapidly. If plant breeders breed for shorter varieties, the amount of less -digestible leaf sheath could become very significant. We found that leaf blade and stem have virtually the same digestibility. As suggested, the proportion of leaf sheath has the greatest effect on the nutritive value of sorghum. Reed: The proportions of plant parts means nothing to a farmer who will feed coarse stovers. The amount of crop residue and the amount of a fraction that can be fed are more important. As such, we should also express our results in yield of the different components per hectare , which may give different relationships. For example, in our trials, medium-height varieties gave a much higher yield of leaf than dwarf varieties, despite having a 250 smaller proportion of leaf in the straw. If you are feeding animals you may want the quantity, not the proportion, except if you were to grind the entire residue and feed it. But when grazed in the field, the leaf fractions are preferred and are of higher nutritive value. 251 SESSION 3 THE EFFECT OF GENOTYPE AND ENVIRONMENT ON THE NUTRITIVE VALUE OF CROP RESIDUES General discussion McDowell: The four papers presented in this session emphasised methodology and genetic and environmental effects on the nutritive value of crop residues. We should focus our discussion on how the methods relate to specific types of residue rather than on the relative merits of the different methods . We heard yesterday about the quantity and potential of crop residues but very little on the effect of environment on the nutritive value of crop residues. Berhane: Has any high-yielding variety been rejected because of low straw quality? 0rskov: No, I do not think so because it is only in the last few years that we have realised that there are large differences in straw nutritive value among varieties. Fussell: In India, a high-yielding millet variety, WC75, had a better acceptance because it had better straw quality. Gupta: WC75 is improved material from an introduction from Nigeria. We just heard that pearl millet in West Africa, especially Niger, is not accepted by cattle because of poor quality of the stems. However, similar material is used by farmers in India as stored cattle feed. This could be due to cultural differences and not because of the crop . We 253 Reed: McAllan: Reed: McAllan: should not generalise that millet is not a good crop for feeding animals on crop residues. The difference between West Africa and India in the use of millet crop residue may be related to cultural differences , but we cannot rule out the possibility of differences in nutritive value . In groundnuts , there is a large difference In the incidence of foliar diseases and their effects on the nutritive value of the crop residue. ICRISAT is breeding for resistance to foliar diseases in groundnuts and this would increase the quality of crop residue by reducing leaf loss. Groundnuts normally retain leaves in the absence of foliar diseases and the nutritive value of the crop residue can be very high. Reed showed differences in digestibil ity of sorghum grown at different sites and suggested that temperature was important. Barry, in Australia, grew lotus in two areas and the tannin content was markedly higher in the lotus grown on low- fertility soil. Has any work been done on the effect of soil fertility in sorghum? I cannot eliminate soil fertility as a factor, although we applied N and P at moderate levels at both sites. Trace elements or soil pH could have had an effect. Certainly temperature and soil effects are important and lead to genotype by environment interactions . It is not surprising that we find large variation in nutritive value within a species if all these condi- 254 Reed: Pearce : McAllan: Pearce : Nordblom: Thomson: tions are not controlled. How can you breed for something you do not know how to control? Pigmentation is a genotypic character istic. Some genotypes respond by producing greater pigmentation, others do not respond. The non-bird- resistant varieties do not produce the pigmentation and the difference between the sites was very low. Plants respond to differences in soil fertility by altering their rate of growth. Slow- growing plants tend to accumulate more secondary metabolites than fast-growing plants. Could this have caused the differences observed by Barry? No, they were absolute effects. The lotus were harvested at maturity. They can be harvested at maturity and still have different rates of growth at a critical point in time. I want to respond to the question of whether any varieties have been rejected on the grounds of residue quality. In Egypt, a traditional wheat variety is not being replaced by new, improved varieties because of lower quantity and quality of their crop residue. They were improved in terms of the breeders0 objective of higher grain yield but rejected by farmers because of quality and quantity of crop residue. We have seen considerable contrast among the four papers presented during this session in the approach used, from the very animal -oriented approach we use at ICARDA to the much more 255 detailed approach of Dr. Pearce, looking at individual components . At ICARDA we will continue the animal work and introduce the laboratory work. I feel it is important to have a solid animal input in this research. We should consider national programmes and universities in addition to international centres when discussing research methods . Animal evaluations are often more appropriate where complex and expensive materials are difficult to obtain. Yilma: I think the search for better quality in crop residues will be possible for the plant breeder as long as it does not compromise agronomic and yield attributes . We have seen that there is variation among cultivars and crop species in straw quality and traits that determine straw quality such as morphology. We have to determine the difference between local cultivars and improved cultivars in quality of crop residue. We need more information on why farmers grow a particular cultivar and the importance they place on feed ing crop residue. Can simple and specific criteria, either laboratory or animal, be established that can be incorporated into a breeding programme for looking at straw quality? Alter natively, can we describe an ideal ecotype in terms of morphological proportions, height, maturity, tiller ing etc? These are things that a plant breeder would ask. Van Soest: A particular set of factors will be unique to each plant species . We need 256 to determine the limiting factors in relationship to the desired nutritive value of the plant. McDowell: It seems that the plant breeder is looking for a recommendation on phenotypic characteristics of the plant that can be selected to meet animal needs. On the other side, there are the laboratory techniques that indicate that this may be mis leading. We need a close integration between the plant and animal scientist so that we can begin to develop an indexing system that could also include cost factors for evaluating crop varieties . Much more effort is required to develop these indices , including research on the effects of preservation and time of harvest. Dr. Pearce , have you looked at the effects of early harvest and artificial drying on preserving the solubles in residue fractions? Pearce: We have thought of this but grain drying under our conditions is too expensive. Grain harvest and the length of the period between grain maturity and harvest is determined by weather conditions. McDowell: Would you recommend picking up the straw the day after combine -harvesting and bailing it to reduce respiration and maintain higher levels of frue tans? Pearce: No, by the time the plant has obtained that low a moisture content it is dead and respiration is finished. But this is not the case for irrigated rice, which is still green and actively 257 growing after harvest. 0rskov: Reed made a good point, that we need to use different criteria for each objective. We have to consider yield of different parts of the plant and whether animals are allowed to feed selectively. The message to the plant breeder is that there is no golden answer that will apply to everything. We have to be flexible and think about why we are using the method. Schildkamp: Crop residues are used primarily for maintaining animals. Animal nutri tionists should not necessarily look for the highest nutritive value but rather stress that crop residues should not fall below a certain standard below which animals cannot use the material for maintenance. 258 SESSION 4 Perspectives and implications for crop improvement programmes GENETIC SELECTION FOR IMPROVED NUTRITIONAL QUALITY OF RICE STRAW- -A PLANT BREEDER'S VIEWPOINT 1 2Gurdev S. Khush , Bienvenido O. Juliano and Domingo B. Roxas 1. Principal Plant Breeder, Plant Breeding Department 2. Chemist, Cereal Chemistry Department 3. Postdoctoral Fellow, Asian Rice Farming Systems Network International Rice Research Institute (IRRI) , P.O. Box 933, Manila, the Philippines. INTRODUCTION In South and Southeast Asia, the primary agricul tural activity is crop production. Plant breeders are engaged in increasing crop productivity per unit area per unit time and in improving grain quality. Straw quantity and quality have been secondary considerations, except as they directly affect crop yield, such as in resistance to insects, diseases and lodging (Khush and Kumar, 1987). Plant breeders are becoming increasingly aware of the need for whole -plant utilisation, and hence of the need to improve the utility of crop residues (Rexen and Munck, 1984) . Ruminant live stock in the rice-producing areas of Asia are dependent on rice straw for part of their nutrient requirements during the cropping seasons and in dry or drought periods (Doyle et al, 1986). But the biodegradability and voluntary intake of rice straw by ruminants are low. The feeding value of rice straw can be improved by treating it with alkali or urea, but genetic improvement of straw quality would be a cheaper and more logical 261 approach. However, feed value should be improved without reducing grain yield and quality. Harvest straw (upper 40-50 cm below the panicle neck) is the most economical fraction of the rice crop residue, since it is already collected and partly dried in threshing areas. Stubble is either burned or ploughed under. We discuss here collaborative research at IRRI examining the feasibility of improving the feed value of rice straw for ruminants. METHODS Dry-matter, crude-protein and organic -matter contents of the straw of various rice genotypes were determined using AOAC (1970) procedures. Neutral -detergent fibre (NDF) , cellulose, lignin and silica contents were determined according to Goering and Van Soest (1970). In vitro organic- matter digestibility (IVOMD) was measured as described by Minson and McLeod (1972) . The rumen fluid was taken from a fistulated buffalo fed a rice -straw-based diet supplemented with a concen trate mix containing 15% crude protein at 1.0% liveweight. Cellulase solubility (in vitro dry matter solubles, IVDMS) was estimated at the Tropical Development and Research Institute (TDRI) , London, by the method of Goto and Minson (1977). VARIATION IN COMPOSITION AND IN VITRO DIGESTIBILITY Variations in chemical composition and in vitro digestibility of rice straw have been summarised by Juliano (1985) and Doyle et al (1986). 262 Varietal differences have been suggested by many researchers, but others have reported little or no variation. Rice straw contains less lignin but more silica and oxalic acid than other cereal straws (Van Soest, 1981; Juliano, 1985). Various morphological, chemical and environ mental factors affect the nutritional value of cereal straws (Doyle et al , 1987; Neilson and Stone, 1987; Nicholson, 1984; Pearce, 1986; Preston and Leng, 1987; Van Soest, 1982). These include cell-wall content; content of lignin and silica; ratio of leaf blade, leaf sheath and stem; length of harvest straw; soil fertility and added fertilizer level; soil moisture and degree of senescence of straw at harvest; growth duration; resistance to pests; and plant height. Cell contents (neutral-detergent solubles) are more readily digestible than cell walls, measured as neutral -detergent fibre (NDF) (Van Soest, 1982). Lignin and silica are reported to reduce the digestibility of rice straw (Van Soest, 1981). However, manipulation of the silica content of three rice varieties by hydroponics did not substantially change the in vitro organic - matter digestibility of the total straw at harvest (Balasta et al , in press) (Table 1). Thus, lignin is probably the most important factor that limits digestibility of rice straw in ruminants (Neilson and Stone, 1987) . Harvest straw is made up of leaf blades , leaf sheaths, the stem and the panicle rachis. The proportions of these components are affected by straw length. In the Philippines, straw is cut 40-50 cm below the base of the panicle to facili tate holding during threshing. The stem contains less ash and protein but more cellulose than the 263 4(ssazd01)•[«3"e3oB4jefiraoanooUOoK1"X4jp=oQ'UOoB o39Afl CI l El 60o 6'T l 6o 60 o60 60» Z4 o1» I4 11» Zo »1 60 £1 60 Io ♦o 11 »o 6€» V( 1'lt o» oo 1» 11 1-* f** to O31 CO »V1 601 oo» oo 81 60 CX) o) (Z) both* U) BO4JI1o (r) "1I1* (X) BDtf1o (J) apniO awoAi apiuo awoAi apruo OWOAI spna" OWOAI oQ9161oQ9161oM161ort1161 9EHI 11HI Z"3HI 9EHI o1)6060 o60 o1 ooz o1 (Uldd)O13BJ3U""UOOO o Xjjsdoaj UOoB"o KjatJBA •BofoisjspA"Tauaaajj1pi iAXue»*Uodoa Xtoun jos xHIJ°ib3o"AJBHjoX}t-q-isaoTp.i G s x -o c .r-* c u 0ffl ul> til as a)« 8 I S % a o M a. iT| tO tO «o Co r-t oo H N 00 CN 00 00 *£> CO 00 CN CO u"i CO CO Co t~i *0 J3 5 rt *< Xl cfl w ■a O h w XI4-1 £4J W c ** J-! VI T> 0) 01 s^ w n) M c 1) a s at N■■00 Tl 0 £ o B InQ 2 EC > u Zl-H M 270 FEEDING STUDIES In addition to the environment-variety interaction on the chemical composition and IVOMD of rice straw, the correspondence of IVOMD to feed value (voluntary intake and in vivo digestibility) needs to be verified. Rice stubble with higher IVOMD than harvest straw (35 vs 25%) showed lower intake and digestibility when fed with concentrates to sheep and goats (Winugroho, 1986). However, among five Thai rainfed lowland rice varieties with similar IVOMD (45-51%), one variety showed higher organic-matter digestibilities in sheep than the others, although voluntary intakes were similar (Cheva-Isarakul and Cheva-Isarakul , 1985a; 1985b). IR 36 and IR58 were multiplied at the IRRI Experimental Farm in the 1986 dry season to produce enough harvest straw and stubble for feeding trials with growing cattle. IVOMD was similar in IR36 harvest straw and stubble and IR58 harvest straw (Table 6) . Voluntary intake and digestibility of the three samples were also similar (Table 6). Initially, intake of IR58 harvest straw was less than that of IR36 straw but after a week of feeding intakes were similar. We need to determine the minimum difference in IVOMD that would be reflected in a significant differ ence in in vivo digestibility in ruminants. GENETIC SELECTION FOR NUTRITIONAL QUALITY OF STRAW The results presented show that chemical composi tion and digestibility of straw varies among rice varieties. This variability presumably could be exploited to improve the nutritional value of the straw of future varieties. However, rice is grown primarily for grain and, at present, no attention 271 Table 6. Chemical and nutritional properties of IR36 and IR58 harvest straw and IR36 stubble fed to cattle, 1986 dry season. Property Harvest straw IR36 (% dry basis) IT58 IR36 stubble Crude ash 21.7 22.4 26.2 Neutral -detergent fibre 63.4 66.0 64.8 Acid- detergent fibre 54.9 55.6 58.8 Heraicellulose 8.5 10.4 6.1 Cellulose 35.9 35.7 35.0 Lignin 4.6 4.8 5.5 Crude silica 14.4 15.1 18.2 IVDMD (% of total) 46.2 48.6 44.3 IVOMD (% of total) 49.0 51.8 50.2 Voluntary intake (% of body wt d"1) 1.6 1.9 1.9 In vivo dry-mat digestibility iter (%) 39.0 43.0 45.0 1. Measured on growing cattle fed with rice straw/stubble and supplemented with concentrated mix at 1% of body weight. Differences among means were not significant. Source: IAS/UPLB- IRRI (unpublished data) . is paid to the nutritional quality of the straw. With the present emphasis on increasing grain yield it is unlikely that any institution will undertake a selection programme to improve the nutritional value of straw but plant breeders may be persuaded to evaluate their advanced breeding lines for the nutritional value of the straw. Other traits being equal, plant breeders could then select lines with better nutritional quality 272 of straw. However, availability of simple screen ing techniques for evaluating the straw quality of breeding materials is a prerequisite. SUMMARY The wide variation in the ratio of leaf blade: leaf sheath: stem, chemical composition and IVOMD of harvest straw suggests that varietal differences in straw nutritional quality exist. However, environmental factors significantly affect IVOMD. Only after the environmental influence on IVOMD is understood and minimised can effective IVOMD screening be justified in a rice breeding programme. The screening method chosen should correlate with in vivo nutritional value of harvest straw. When selecting for straw quality, we must at the same time maintain or even improve grain yields and grain quality, the major goals of current rice breeding programmes . Acknowledgements The results reported here are from a collaborative project between IRRI , the Institute of Animal Science, University of the Philippines at Los Banos and the Department of Biochemistry, La Trobe University, Bundoora, Victoria, Australia 3083. The research was carried out under Australian Centre for International Agricultural Research Project 8373 with the School of Agriculture and Forestry, University of Melbourne, Parkville, Victoria, Australia 3052. Screening for varietal difference in in vitro digestibility of harvest straw is a cooperative study (project A1482) with the Animal Feeds Section, Tropical Development and Research Institute, London WC1X 8LU, England. 273 REFERENCES AOAC (Association of Official Analytical Chemists). 1970. Official methods of analysis . 11th ed. AOAC, Washington DC, USA. Bainton S J, Plumb V E, Capper B S and Juliano B O. 1987a. Botanical composition, chemical analysis and cellulase solubility of rice straw from different varieties. In: Winter Meeting of the British Society of Animal Production. March 1987. Bainton S J, Plumb V E, Drake M D, Juliano B 0 and Capper B S. 1987b. Effect of physiological and morphological characteristics on in vitro cellulase solubility of different varieties of rice straw. In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1986. Proceedings of the Sixth Annual Workshop of the Australian- Asian Fibrous Agricultural Residues Research Network, Los Banos , Laguna, Philippines, 1-5 April 1986. International Development Program of Australian Universities and Colleges, Canberra, Australia. Balasta M L F C, Perez C M, Juliano B 0, Roxas D B and Villareal C P. (in press). The effect of silica level on some properties of rice plant and grain. In: R M Dixon (ed.), Strategies for using crop residues as animal feeds. Proceedings of the Seventh Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Chiang Mai, Thailand, 2-6 June 1987. International Development Program of Australian Universities and Colleges, Canberra, Australia. Cheva-Isarakul Boonlom and Cheva-Isarakul Boonserm. 1985a. Variation in the nutritive 274 value of rice straw in northern Thailand. In: P T Doyle (ed.), The utilization of fibrous agricultural residues as animal feeds . Proceedings of the Fourth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Khon Kaen, Thailand, 10-14 April 1984. International Development Program of Australian Universities and Colleges, Canberra, Australia. Cheva-Isarakul Boonlom and Cheva-Isarakul Boonserm. 1985b. Variation in the nutritive value of rice straw in northern Thailand: II. Voluntary feed intake and digestibility by sheep. In: M Wanapat and C Devendra (eds) , Relevance of crop residues as animal feeds in developing countries . Proceedings of an International Workshop, Khon Kaen, Thailand, 29 November- 2 December 1984. Khon Kaen University, Thailand. Doyle P T, Devendra C and Pearce G R. 1986. Rice straw as a feed for ruminants . International Development Programme of Australian Universities and Colleges, Canberra, Australia. Doyle P T, Pearce G R and Djajanegra A. 1987. Intake and digestion of cereal straws. In: Proceedings of the Fourth Animal Science Congress , Asian-Australasian Association of Animal Production Societies, Hamilton, New Zealand, 1-6 February 1987. Goering H K and Van Soest P J. 1970. Forage fiber analysis . Agriculture Handbook No. 379. Agricultural Research Service, United States Department of Agriculture, Washington DC, USA. Goto I and Minson D J. 1977. Prediction of the dry matter digestibility of tropical grasses using a pepsin-cellulase bio-assay. Animal 275 Feed Science and Technology 2:247-253. Hart F J and Wanapat M. 1985. The effect of conservation of rice straw and stubble on its nutritive value. In: The utilization of fibrous agricultural residues as ruminant feeds project. Annual Report 1984-85. Department of Animal Science, Khon Kaen University, Thailand. Hart F J and Wanapat M. 1986. Comparison of the nutritive value of straw and stubble from rice grown in the north-east of Thailand. In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1985. Proceedings of the Fifth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Bogor, Indonesia, 13-17 April 1985. International Development Program of Australian Universities and Colleges, Canberra, Australia. IRRI (International Rice Research Institute) . 1984. Annual Report for 1983. IRRI, Los Banos , Laguna, the Philippines. IRRI. 1985. Annual Report for 1984. IRRI, Los Banos, Laguna, the Philippines. Juliano B 0. 1985. Rice hull and rice straw. In: B 0 Juliano (ed.), Rice chemistry and technology . 2nd ed. American Association of Cereal Chemists, St Paul, MN, USA. Juliano B 0, Roxas D B, Perez C M and Khush G S. (in press). Varietal differences in composition and in vitro digestibility of harvest rice straw. In: R M Dixon (ed.), Strategies for using crop residues as animal feeds . Proceedings of the Seventh Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Chiang Mai, Thailand, 2-6 June 1987. International Development Program of 276 Australian Universities and Colleges, Canberra, Australia. Khush G S and Kumar I. 1987. Genetic selection for improved nutritional quality of fibrous crop residues of cereal crops - a plant breeder's viewpoint. In: Ruminant feeding systems utilizing fibrous agricultural residues - 1986. Proceedings of the Sixth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Los Banos , Laguna, the Philippines, 1-5 April 1986. International Development Program of Australian Universities and Colleges, Canberra, Australia. Minson D J and McLeod M N. 1972. The in vitro technique: Its modification for estimating digestibility of large numbers of tropical pasture samples. CSIRO Division of Tropical Crops and Pastures Technical Paper 8. Commonwealth Scientific and Industrial Research Organisation, Australia. Neilson M J and Stone B A. 1987. Chemical composition of fibrous feeds for ruminants in relation to digestibility. In: Proceedings of the Fourth Animal Science Congress , Asian- Australasian Association of Animal Production Societies, Hamilton, New Zealand, 1-6 February 1987. Nicholson J W G. 1984. Digestibility, nutritive value, and feed intake. In: F Sundst^l and E Owen (eds) , Straw and other fibrous by products as feed. Elsevier, Amsterdam, the Netherlands . Pearce G R. 1986. Possibilities for improving the nutritive value of rice straw without pretreatment . In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1985. Proceedings of the Fifth Annual Workshop of the Australian- 277 Asian Fibrous Agricultural Residues Research Network, Bogor, Indonesia, 13-17 April 1985. International Development Program of Australian Universities and Colleges, Canberra, Australia. Preston T R and Leng R A. 1987. Matching livestock systems to available feed resources in developing countries . University of Armidale Press, Armidale , NSW, Australia. Rexen F and Munck L. 1984. Cereal crops for industrial use in Europe. Commission of the European Communities, Luxembourg and Carlsberg Research Centre, Copenhagen, Denmark. Roxas D B, Castillo L S, Obsioma A R, Lapitan R M, Momongan V G and Juliano B O. 1984. Chemical composition and in vitro digestibility of straw from different varieties of rice. In: P T Doyle (ed.), The utilization of fibrous agricultural residues as animal feeds. Proceedings of the Third Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Peradeniya, Sri Lanka, 17-22 April 1983. University of Melbourne, Australia. Roxas D B, Obsioma A R, Lapitan R M, Castillo L S, Momongan V G and Juliano B O. 1985. The effect of variety of rice, level of nitrogen fertilization and season on the chemical composition and in vitro digestibility of straw. In: P T Doyle (ed.), The utilization of fibrous agricultural residues as animal feeds. Proceedings of the Fourth Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Khon Kaen, Thailand, 10-14 April 1984. International Development Program of Australian Universities and Colleges, Canberra, Australia. 278 Roxas D B, Aller M G and Juliano B 0. (in press). Changes in chemical composition and in vitro digestibility of straw components from four rice varieties. In: R M Dixon (ed.), Strategies for using crop residues as animal feeds. Proceedings of the Seventh Annual Workshop of the Australian-Asian Fibrous Agricultural Residues Research Network, Chiang Mai, Thailand, 2-6 June 1987. International Development Program of Australian Universities and Colleges, Canberra, Australia. Sharma U, Brillouet J-M, Scalbert A and Monties B. 1986. Studies on a brittle stem mutant of rice, Oryza sativa L. ; characterization of lignin fractions, associated phenolic acids and polysaccharides from rice stem. Agronomie 6:265-271. Van Soest P J. 1981. Limiting factors in plant residues of low biodegradability. Agriculture and Environment 6:135-143. Van Soest P J. 1982. Nutritional ecology of the ruminant. 0 & B Books, Corvallis, Oregon, USA. Winugroho M. 1986. Intake and digestibility of the upper and lower fractions of rice straw by sheep and goats. In: R M Dixon (ed.), Ruminant feeding systems utilizing fibrous agricultural residues - 1985. Proceedings of the Fifth Annual Workshop of the Australian- Asian Fibrous Agricultural Residues Research Network, Bogor, Indonesia, 13-17 April 1985. International Development Program of Australian Universities and Colleges, Canberra, Australia. 279 DISCUSSION Van Soest: Khush : Mueller- Harvey : Khush : prskov: Khush : Little: Capper: Little: Khush : What are the problems connected with low silica levels in the nutrient solutions on which rice plants were grown? Generally low yields . Are phenolic compounds of any significance in rice breeding? Yes, in relation to insect resistance. Are there no relationships between grain yield and straw quality? No clear relationship has been found. Although plant breeders must concentrate on improving grain yields in rice, it is possible that straw quality can be given some attention. Do higher-yielding rice varieties have higher crude protein contents in their straw? Traditional varieties may have about 4% crude protein, rising to 6 or 7% in improved varieties. From the research on rice to date it appears that selec tion for grain yield has not reduced straw quality. However, one problem in investigating rice straw quality is the variability both within and bet ween plots and there seems to be no satisfactory explanation for this . It appears that there is only little genetically determined variation in the nitrogen content of straws. Will it be possible to select for this? The direction breeding programmes take will depend upon priorities and the relative importance of grain and straw. 280 Thomson: At ICARDA the facilities devoted to examination of straw quality are modest and take up only a small proportion of the budget. I consider that it is not beyond the resources of the CG centres to address the question of straw quality. 281 EVALUATING SORGHUM CULTIVARS FOR GRAIN AND STRAW YIELD John Mclntire , Jess D. Reed , Abate Tedla , Samuel Jutzi , and Yilma Kebede . 1. International Livestock Center for Africa, P.O. Box 5689, Addis Ababa, Ethiopia. 2. Institute of Agricultural Research, Nazareth, Ethiopia. INTRODUCTION Cereal lines in breeding trials are usually evaluated on mean grain yield, although attention is sometimes given to yield stability or grain quality. Mean yield is most relevant where there is only one product of interest, such as grain, but may be misleading where there are joint products, especially if uses of the products differ. One such example is sorghum. This paper proposes a method to estimate the trade-off between sorghum grain and straw yield in agronomic trials. First, a theory of the conflict between the two products is described. Second, data from sorghum cultivar trials in Ethiopia are presented. Third, a method of valuing sorghum grain and straw is given. Lastly, conclusions about breeding strategies are drawn. JOINT PRODUCTS AND PRODUCTION EFFICIENCY The conflict between grain and straw yield can be modeled with the theory of joint products (Henderson and Quandt, 1971). Consider a sorghum cultivar producing both grain and straw from a 283 single input, land, as illustrated in Figure 1. The curve in Figure 1 is commonly known as a transformation curve of two outputs as function of one input. The relation describing the outputs of the two products is expressed as an implicit function of land input: 1 - f(g,s) where s is straw, g is grain, and 1 is land. By taking the total differential of this function and setting it equal to zero, one can solve for the ratio of the derivatives with respect to land input- -[ (ds/dl)/(dg/dl) ]- -the rate at which one product is sacrificed to produce the other at a given level of land input. The negative of the ratio of the derivatives is defined as the rate of product transformation. The choice of the point at which to operate along a transformation curve is determined by the prices of the outputs, p(g) and p(s), where 'p' represents market price. Assuming that market prices are fixed, the optimal production point on a transformation curve is that where [p(g)/p(s)] - [(ds/dl)/(dg/dl)] that is, where the ratio of grain price to straw price is equal to the rate of product transforma tion of straw into grain. The ratio of grain price to straw price is the tangent in Figure 1. Two types of efficiency can be analysed with Figure 1. Technical efficiency means producing the maximum amount of either product for a given 284 § -3; 1 -s "a c K 3 2 u a 5 -i 1 1 1 r pieiA mdj|s eiqijsaBiQ 3 285 amount of the other product; that is, a producer who is technically efficient operates at some point on the transformation curve. Allocative efficiency means producing the two products in the right proportions, where those proportions are dictated by the price ratios of the products. A producer who is allocatively and technically effi cient operates at the optimal point on the trans formation curve. Graphically, the optimal point is that at which the price ratio is tangent to the transformation curve, shown by point E in Figure 1. It is possible to be allocatively efficient and technically inefficient, and vice versa. EVALUATING GRAIN AND STRAW Data from sorghum trials conducted by the Ethiopian Institute of Agricultural Research and ILCA were used to test the theory outlined above. Table 1 shows descriptive statistics for grain yield, straw yield and digestibility for sorghums tested at Debre Zeit in 1984 and at Debre Zeit and Nazareth in 1985 (IAR, 1986). Debre Zeit is at 1850 metres above sea level, in the transition zone between the highlands and lowlands of Ethiopia. Nazareth is at 1500 m and has a hotter, drier climate. The sorghum cultivars were evaluated in the field in the usual way. Straw samples of each cultivar were analysed in the laboratory for digestibility (Reed et al , 1987). In 1984, digestibility was estimated for leaves and stems and in 1985 for leaf blades , leaf sheaths and stems. The digestibilities in Table 1 are weighted averages of whole plant digestibility, where the weights are the fractions of each plant 286 Table 1. Descriptive statistics for three sorghum trials . Apparent Grain Straw digest yield (t ha'1) yield (t ha"1) ibility (%) ' Debre Zeit, 1984 Brown sorghums 2.61 5.38 53.6 Red sorghums 2.50 5.97 51.4 White sorghums 2.54 5.18 51.5 Overall 2.55 5.51 52.2 Debre Zeit, 1985 Brown sorghums 4.46 8.37 52.3 Red sorghums 5.72 7.11 55.5 White sorghums 2.94 6.49 54.0 Overall 4.58 8.13 52.8 Nazareth, 1985 Brown sorghums 4.18 5.13 57.3 Red sorghums 3.68 4.93 60.1 White sorghums 0.92 2.80 57.0 Overall 4.00 5.02 57.7 part in the oven-dried straw dry matter (DM) of the plant samples . A more complicated case occurs when straw is fed for an extended period. If straw quality degrades, then its quantity over the feeding period must be adjusted. However, only if there were different rates of decay for different cultivars , would decay affect the comparisons among cultivars. 287 The value of grain for sale is the market price. Market prices for sorghum grain are given in Table 2 for the area around Debre Zeit. There are three possible values of sorghum straw. The first is its market price. The second is its value in maintaining a herd if it is the only feed. In this case, the value of sorghum straw is the value of annual production from the herd, at market prices , divided by the quantity of straw necessary to maintain the herd. This is called Table 2. Unit values of sorghum grain and straw. Grain price (EB kg 1)1 Straw price (EB kg" ) 2 Average (Oct 1984- Oct- March- July- Sept 1985) Jan April Sept 0.53 0.50 0.50 0.60 0.23 0.20 0.20 0.30 54.3 80.0 0.34 0.29 0.29 0.44 1.50 1.70 1.70 1.36 3.50 3.43 3.13 3.94 1.23 1.30 0.98 1.42 1.97 1.90 2.00 2.00 0.57 0.50 0.66 0.55 0.05 0.05 0.05 0.05 Average straw digestibility (X) Sorghum digestibility as X of teff digestibility -1 3 Digestible straw price (EB kg ) Grain/straw price ratios Average market value Average maintenance value Average supplementation value Meat price (EB kg" LW) Milk price (EB kg"1) Manure price (EB kg ) 1. EB - Ethiopian Birr. 1 US $ = 2.07 Ethiopian Birr. 2. The average sorghum straw digestibility is the mean of the three trials. 3. Digestible sorghum straw price is estimated by multiplying the teff straw price by the sorghum digestibility as a percentage of teff digestibility. 288 the average maintenance value in Table 2 . The third is its value as a supplemental feed. In this case, assume that maintenance feeding re quirements are satisfied from pastures and crop residues and that sorghum straw is used as a supplement for milk production. An energy balance model of milk production can then be used to calculate the value of the straw (Sandford, 1978) . This is called the average supplementation value in Table 2. (Details of the calculations of the maintenance and supplementation values of sorghum straw are given in Appendix 1) . Table 2 gives illustrative values of sorghum grain/straw price ratios using the three methods. The highest grain/straw value ratio- -that which places the lowest value on straw- -is the mainte nance value. The lowest ratio --that which places the highest value on straw- -is the supplementation value . The value of a cultivar is expressed in equations (1) and (2) . (1) V(g) = p(g)*q(g) (2) V(s) - p(s)*q(s) where V=value per hectare, p=price per kg, g=grain, q=quantity in kg per hectare, and s—straw. The quantity of animal production for a given straw consumption is given in equation (3). (3) q(a) =f(q(s)) where q(a) is a quantity of animal product. Equation 3 can be understood as a very general representation of any of the three methods of calculating the productivity of straw. 289 The total value of a cultivar is (4) V(t) - V(s) + V(g) where V(s) and V(g) are estimated from equations (1) and (2), and t-total. Table 3 gives typical values for the total values of cultivars in the three trials . THE CONFLICT BETWEEN GRAIN AND STRAW YIELD The transformation curve in Figure 1 illustrates the conflict between grain and straw yield. To estimate the curve, the mean of each cultivar 's grain and digestible straw DM yield was calculated across replicates at each site. Then, assuming Assumptions are that seed rates do not differ significantly between cultivars, so that net grain output per hectare is a linear transfor mation of gross output. All grain is sold and evaluated at market prices. Grain value would be affected if some is retained for home con sumption. However, the results would be af fected only if the fraction retained differed significantly between cultivars. Third, it is assumed that there are no market price differ ences between sorghum grain qualities, as shown by grain colour. Such differences would have an effect on the inter -cultivar compari sons. Fourth, no mixed straw sale/ straw feeding strategies are allowed. All straw is assumed to be sold, or to be fed for one purpose. Mixed strategies would only affect the comparison between cultivars if the pro portions sold and fed differed between cultivars . 290 : Ni i i a iM CM CM *r^o0»n(NON-0U-i 00 r. O r«r«r>>or-e^P>0>o io ga o 0 o> oa cm r- "•on « H « O r-< 0 oa on oa oa cc o o — 3 C i ifl CO -i r0 C* n e* O O n CO O .-i «-i CM N n 00 O CO iM CO N 04 M « M 3 a. m 0 0 r» CO CO _ a> « in o 0 m « Ou'itoo0ir0i.!0'-i'^.^r0i-jo c- 00i t* O 0O r- ■• CS >rt 0O i-i K •0■ •0> 00>"" — CMtM MCMCMCMCMCMtMMrtCMCMr^CMCM^CMCMCM -0 *M CM MKMXMMMMfQ oq ui oe 3 en si >■ 3 9 CM X 291 that straw yield was zero if grain yield was zero, the Pythagorean theorem was used to calculate the maximum distance from the origin at each site by finding the maximum of the sum of the squares of grain and straw DDM yield for each cultivar, denoted by: ? 2max(grain^ + straw DDM^ ) where 'i' is the cultivar index. This maximum distance was the most efficient combination of grain and straw production for cultivars at a site . Using that maximum distance, the efficient straw yield (S^) corresponding to every grain yield was calculated by (sp - [max(grain2 + straw DDM2) - grain^]1/2 Plotting the efficient straw yield against actual grain yield gave the transformation curve in Figure 2 for pooled data from the three trials . The slopes of the transformation curves, which are interpreted as the losses in digestible straw yield with an increment in grain yield, are shown below. They were estimated for each trial by regressing the efficient straw yields on actual grain yield and on actual grain yield squared. Grain yields Mean Maximum Debre Zeit, 1984 Debre Zeit, 1985 Nazareth, 1985 0.69 -1.10 0.72 -1.33 0.55 -0.88 292 o■Si -c■« .5 .0 S c o o 2 ° E — c «>0& i1> ainc bro red whi trai cur • «§•■•« 1 /•• ■ ■ • •• • :• ••• - • A • * / • • « • • •* 2 - 2 ■ < Q„°- »f i i I 1 i i i i o U3 a GO CD o o CO Is-' q o o o to q o <\i — U 3 00 293 For example, at Debre Zeit in 1984, at the mean grain yield of 2.55 t ha" , a 1 kg increase in grain yield would have reduced sorghum straw DM yield by 0.69 kg; at the maximum grain yield of 3.58 t ha, a 1 kg increase in grain yield would have reduced sorghum straw DM yield by 1.10 kg. CHOOSING EFFICIENT CULTIVARS Transformation curves can be used to choose cultivars that are technically and allocatively efficient. Technical inefficiency is measured by the value of the straw yield lost by not producing on the transformation curve for a given grain yield; it is equal to efficient straw yield minus actual straw yield times straw price, i.e. (SL - Si)*p(s). In terms of Figure 1, an increase in alloca- tive efficiency, represented by the movement from point A to point E on the curve, raises grain yield and reduces straw yield. A movement from point B to point E reduces grain yield and raises straw yield. Both movements are increases in allocative efficiency. The slopes of the estimated transformation curves at the mean grain yields were between -0.55 and -0.72. The absolute values of those ratios are smaller than the grain/straw price ratios, implying that an allocatively efficient cultivar would have a higher grain yield and a lower straw yield than any tested in these trials. Therefore, allocative inefficiency is measured against the standard of the cultivar having the highest grain/ straw ratio, not against the allocatively effi cient price ratio. Allocative inefficiency is 294 equal to the value of the grain yield lost (gained) in moving along the transformation curve minus the value of the straw yield gained (lost) . Table 4 shows the costs of technical and allocative inefficiency in sorghum cultivars in the three trials. Technical inefficiency- -produc ing too little straw at a given grain yield- -is the major cost of inefficiency in these trials. In practice, only cultivars with high grain yields are usually included in extension program mes. Such programmes concentrate on one part of the grain yield distribution and neglect the over all value of the plant. What are the consequences for farm income if only cultivars with higher grain yields are selected for extension? Cultivars were ranked by grain yield, by the total revenue at market prices from grain and digestible straw production, by technical effi ciency, and by allocative efficiency (Table 4) . These criteria were chosen because grain yield is probably the extension criterion; the value of production is the overall return to the cultivar; technical inefficiency is a measure of the return to raising straw yield while holding grain yield constant; allocative inefficiency is a measure of the return to reallocating dry-matter production in line with the prices of grain and straw. Spearman rank correlations were as follows : Grain Technical yield efficiency Revenue 0.878** Technical efficiency -0.164 Allocative efficiency 0.313** 0.654** ** Significant at P<0 . 01 295 0 23 21 Mean s.d. 1.00 2.08 2.0 1.0 2.0 3.01 2.08 2.28 2.0 2.N 2.0 2.0 2.0 2.0 2.0 2.N 3.15 20 2.08 l.fO 3.r 2.0 J.S2 2.0 255 052 1368 2308 203 200 200 2308 200 033 033 208 230 2005 083 2568 200 80 280 20■8 88 2050 2■55 033 2855 206 2350 308 508 05 00 00 230 30 0 0 01 08 330 03 08 3N 0 350 693 00 00 630 52 50 08 06 60 05 10 080 20 08 03 30 302 06 03 156 20 28 N3 285 0 10 388 00 132 20 155 5.0 3.03 5.35 0.13 5.50 3.0 0.8 3.56 3.08 3.0 3.0 1.0 2.0 3.0 68 5.52 5.0 5.60 6.0 528 60 60 508 28■ ■50 133 030 000 030 005 020 300 303 3028 382 300 00 300 203 309 5015 030 003 008 5i00 020 00 510 085 2333 80 60 3N 080 02 80 583 00 00 00 881 1500 30 305 100 30 83 30 30 00 0 03 05 02 002 1■30 00 00 N8 08 80 6N 01 308 523 82 00 06 853 008 053 08 0 210 2■■ 0■ 00 81 06 00 553 30 0 0 60 330 00 00 898 305 983 N3 00 02 368 00 80 20 30 00 0 560 03 20 50 O 80 80 60 00 182 00 13N N8 005 030 208 0N 060 150 086 030 208 108 033 808 00 00 0 105 00 50 209 209 150 50 00 208 300 000 052 203 00 08 202 303 002 302 08 80 0N 200 063 30r 003 8N 230 00 23N 00 023 00 30 3.56 023 5S3 314 3.0 20 3.8 20 0.38 0.0 3.0 3N 085 0.33 20 5.8 0.8 035 ■0 ■0 50 315 0 30 18 Table4.Costsofinefficiencynsorghumcultivars. Debreisit,08* De[qeitit,085 i.[qett,085 GrainTotal yieldvalue Cultivar(tha"4)EMha Inefficiencies (EBha"1) TechAlloca0 nicaltIv GrainTotal yieldvalue (tha04)(EB/ha) Ineffici nci (EBha~) Tech0Alloca0 nicalt ve Ineffici nci (EBha"1) GrainTotal yieldvalueTech0Alloc (tha")(EB/ha)nicaltive TotalvalueIscalcul tedusingthgeera edigegtibl=r humstr wp iceandthge gegrap icf mTab2. Selecting cultivars for grain yield would, in effect, select for revenue and for allocative efficiency. However, it would tend to select cultivars that are technically inefficient, in that they produce too little straw for their grain yields . CONCLUSIONS In Ethiopia, grain/straw price ratios are so high that continued emphasis on grain yield at the expense of straw is justified. The estimated trade-off between grain and straw yield is small enough that much higher grain yields would have to be achieved before that trade-off began to reduce total revenue from sorghum production. However, one study from central India (Walker, 1987) shows lower grain/straw price ratios, which would favour cultivars with higher straw/grain product ratios. There was a significant (P<0.01) positive correlation between cultivar rank on grain yield and rank on revenue. With few exceptions, those cultivars having the highest grain yields would not suffer a straw yield penalty large enough to make them inferior to low grain yielders , which gave more straw. This suggests that extension programmes could, like breeding programmes, safely insist on grain yield, if the market prices of grain and straw reflect their values to the farmer. If the choice is among sorghum cultivars to include in a screening programme, these data imply that straw yield would probably not be relevant. Of the 10 cultivars yielding more than 5.5 t of grain DM ha" , eight ranked among the top 10 on revenue and four ranked among the top 10 on straw 297 yield. The trade-off between grain and straw yield would not dramatically affect decisions about including cultivars in a screening programme . Furthermore , the low revenue ranks of some cultivars might simply reflect selection for high grain/straw ratio, and not a necessary physical trade-off between grain and straw yield. The situation might be different in an extension programme. Where the choice is among cultivars to extend to farmers in different environments and with different preferences, the decisions to extend a cultivar with high grain yield (e.g. #21 in 1984, highest grain yield and second lowest straw yield) would have to be chosen carefully because of the obvious possibility that its low straw yield would impair its adoption where the grain/straw price ratio is lower than that used in this paper. To take the converse case, it is unlikely that a high straw/low grain cultivar would be adopted simply because of its superior straw yield. Many cultivars are technically inefficient, in that they produce much less straw, at given grain yields, than do the more efficient cultivars tested. Major gains could be made by raising straw yields to efficient levels while preserving grain yields . The general advantage of grain over straw would be changed if sorghum straw is a supplement to a maintenance regime of pastures. In that case, the grain/straw price ratio falls and it becomes more profitable to select sorghum cultivars with lower grain/straw ratios. However, it is unlikely that peasant farmers have sufficient pastures for maintenance: they are thus obliged to use crop residues for low productivity 298 maintenance as well as for higher productivity supplementation. The apparent differences in straw yield, straw digestibility, leaf and stem digestibility and leaf/stem ratios across cultivars (and, in the case of stem dry matter, across grain colour groups) need to be investigated systematically. It is possible that overall digestible straw yield is not the most relevant criterion to use in considering straw yield in such trials. It may be that some cultivars with high leaf/stem ratios could be exploited to provide highly digestible feed at key times in the cropping season when other sources of feed are scarce. Acknowledgments The authors acknowledge the helpful comments of Stephen Sandford, Gil Rodriguez, Jr., Ray Brokken, and P. N. de Leeuw on earlier drafts. REFERENCES Gryseels , Guido and Anderson, Frank M. 1983. Research on farm and livestock productivity in the central Ethiopian highlands: Initial results, 1977-1980. ILCA Research Report 4. Henderson J M and Quandt R E. 1971. Microeconomic theory: A mathematical approach. McGraw- Hill, New York. IAR (Institute of Agricultural Research). 1986. Ethiopian Sorghum Improvement Program Progress Report 13. Addis Ababa. Reed, Jess, Abate Tedla, and Yilma Kebede . 1987. Phenolics, fibre and fibre digestibility in the crop residue from bird-resistant and non 299 bird resistant sorghum varieties. Journal of the Science of Food and Agriculture. 39:113- 121. Sandford, Stephen. 1978. Some aspects of livestock development in India. Pastoral Network paper 5c. ODI , London. Walker T S. 1987. Economic prospects for agroforestry interventions in India's SAT: Implications for research resource allocation at ICRISAT. ICRISAT Resource Management Program, Economics Group, Progress Report-79. Patancheru, India. 300 APPENDIX 1. STRAW VALUE CALCULATIONS. End of LW per Off takeyear LW class Herd structure No. (kg) (kg) (kg LW) Breeding cows 1.0 250 250 20 Calves 1.0 100 100 8 Heifers 1.0 167 167 13 Males 2.0 312 625 50 Total 5.0 1142 91 1. Assumed offtake rate of 8.0% for all classes. Animal productivity parameters Annual LW in herd (kg) Calving rate (%) Milk production per lactating cow per year (kg) Base intake of digestible dry matter (DDM) (% LW per day) Annual DDM intake per herd (kg) Percentage of intake converted into manure 1142 50.0 400 2.5 10 418 20.0 Maintenance model, assuming all intake is from crop residues Annual LW offtake (kg) Annual milk production (kg) Annual manure production (kg) Value of draught oxen for grain production (Birr) Annual value of production from herd (Birr) Average straw value (Birr kg"1 DDM) 91 200 2084 384 782 0.08 301 Supplementation model, assuming maintenance is from pastures Potential milk yield (kg cow" yr" ) Intake of DDM per cow per year for maintenance (kg) Intake of DDM per cow per year for growth Assumed extra daily intake (% of base intake) Intake of DDM growth (kg cow" yr" ) Average straw value (Birr kg"1 DDM) (from energy budget) 1200 2281 33.0 3034 0.46 Energy budget for cows in milk Feed intake (kg DDM day"1) Energy content of sorghum straw (kcal) Energy intake (kcal) DM (% fresh feed weight) Sorghum straw digestibility (%) Metabolisable energy (ME) as percent of net energy (NE) ME converted to NE in milk (%) NE of milk (kcal litre"1) Average annual milk price (Birr litre"1) Energy value of straw (kcal kg"1 DDM) Milk production (litre kg"1 feed) Average straw value (Birr kg"1 DDM) 8.31 4000 33 250 50.0 54.3 87.5 70.0 830 0.57 666 0.80 0.46 302 DISCUSSION Witcombe: Can you explain exactly how the parameters grain and digestible straw yield relate to your terms technical and allocative efficiency? McIntire: The terms are products of the first two parameters Nordblom: Your analysis appears to ignore the differentiation of plant parts in terms of nutritive value. McIntire: The digestible straw yield is, in effect, the weighted average of the fractions. There is, however, much more to be gained from exploiting differences in straw yield than differences in digestibility. Witcombe: How do you make the final decision to select amongst the varieties that are similar in grain yield? McIntire: The final choice depends upon prices. Jenkins: The prices may vary considerably between seasons. How do you take this into account in your analysis? McIntire: One can use long-term price expectancy figures . McDowell: You have not included the benefit of preserving capital as live animals in your estimate of the value of straw for maintenance . Mclntire: Market prices are generally higher than the maintenance value, so this aspect is not important. McDowell: Maintenance implies a minimum value for straw digestibility so that your parameter of digestible straw yield is not meaningful . Berhan: There are other uses for sorghum stalks, such as house construction, 303 which should be considered in the model . McIntire: These are included in the market price. Nordblom: This is only true if there is no market failure. Reed: In parts of India the supplementation value is considerable and prices may be higher than you suggest. 304 SESSION 4 PERSPECTIVES AND IMPLICATIONS FOR CROP IMPROVEMENT PROGRAMMES General discussion 0rskov: We have not so far considered alternative uses of straw for industrial purposes. Van Soest: The hemicellulose fraction which can be utilised by ruminants is of no value for paper making. Reed: There are many issues relating to variation in straw quality which remain unresolved. This requires co operation between animal nutritionists and plant breeders in research programmes to resolve the problems . Jenkins: It is unlikely that any efforts will be made to breed for straw quality in Western Europe. Goe: For developing countries we should start examining how farmers value their crop residues and how they utilise them. Witcombe: ICRISAT has conducted such investigations with millet in India and found that farmers knew which varieties yielded more stover. As a consequence it is necessary to screen for crop residue yield and quality. In the ICRISAT millet breeding programme we are selecting for high fodder yield. Fussell: It appears that the introduction of new sorghum and millet varieties in West Africa has resulted in a reduction in biomass per hectare and 305 there has been a reduction in leafiness . prskov: At what stage in a breeding programme would you approach farmers to get their views on what they would require in terms of straw yield and quality? Jenkins: I do not think this would be necessary at any stage in Western Europe. Gupta: Plant breeding programmes will vary in their priorities in different parts of the world according to the relative importance of crop residues . 306 SESSION 5 Recommendations and future prospects for plant breeding to maintain or improve the nutritive value of crop residues REPORTS OF WORKING GROUPS GROUP 1 Topic: The effects of crop improvement programmes on the nutritive value and utilisation of crop residues for feeding ruminants . (a) Quality 1. Effects of crop improvement programmes on residue quality are probably random. Plant breeders have not, in the past, placed any emphasis on straw and stover quality. This probably applies to all CG Centre programmes and to the NARSs. More examples can be found of crop residue quality being reduced than examples of improved residue quality. However, this is probably only because non-adoption of a new variety due to poor crop residue quality is more noticeable than increased adoption because of better stover or straw quality. Examples of "improved" varieties with poorer residue quality than locally grown varieties include Beecher barley in the ICARDA region, improved wheats from the Egyptian natural program, and maizes in Mexico . The only case of a non- random effect on crop residue quality is that of selecting for bird-resistance in sorghum. 2. The following points were considered to be notable by the group: 309 2.1 In most crop species there is a large range of digestibility and proportions of plant components . 2.2 Voluntary intake is an important aspect of crop residue quality and must be considered by crop improvement programmes . 2.3 Chemical treatment of crop residues to improve their nutritive value has not been well accepted because of costs, labour requirements , the need to handle toxic chemicals, and unreliable results (b) Quantity In several major cereals the introduction of dwarfing genes has reduced straw quantity, but this effect may be offset by the greater use of fertilizer on dwarf varieties, which increases biomass yield. However, economic factors will not always allow the use of higher inputs , particularly with lower-value crops on resource- poor farms . It is only desirable to increase the quantity of residues produced in mixed farming areas. In developed countries, where livestock production tends to be concentrated in regions away from crop production, large quantities of crop residues are undesirable. 310 GROUP 2 Topic: Factors that limit the nutritive value of crop residues and research that is needed to define and overcome the limitations in nutritive value Factors affecting the nutritive value of crop residues o Level of voluntary intake o Digestibility o Animal ability to select leaf material o Amount on offer o Anti -nutritional factors Factors affecting voluntary intake o Fibre content o Degradation rate o Crude -protein content o Palatability factors Areas needing research o Effect of time of harvest on voluntary intake and digestibility of straw o Effects of storage, particularly with respect to termites, rain damage, use of NaHCOo under stacks o Effects of stack construction o Effects on nutritive value of stress, particularly low soil fertility and drought, and their relationships with phenolics. o Effect of level of feeding, i.e. what production level represents optimal utilisation of feed resources o Effect of supplementation with legumes and forages 311 o Methods for assessing the volume and density of stacks so that the farmer can plan feeding strategies and does not run out of higher quality crop residues because of their higher consumption. o Evaluation of near- infrared-reflectance techniques , including determination of phenolics and crude protein o Studies of feed preference and intake o The NaOH/back titration test for measuring the extent of carbohydrate/1 ignin bonding needs to be evaluated for different crop species o Investigation of Maillard reactions in rice straw 312 GROUP 3 Topic: The effects of increased utilisation of crop residues for feeding ruminants on productivity , income and stability of smallholder farming systems. Crop residues are very important in smallholder systems but in many cases the existing resources are used to the maximum extent. Therefore emphasis needs to be put on increased yield and quality of crop residues and the use of supplements. The trade-offs between use of crop residues as feed or as fuel and construction materials need examination. The increased use of dung as a fuel and its impact on soil fertility should be examined in relation to other sources of fuel, such as multipurpose leguminous trees. The effects of practices such as leaf stripping on fodder and grain yields need studying. 313 GROUP 4 Topic: The influence of the amount and value of crop residues on farmers' decisions to grow improved crop varieties . These considerations mainly affect integrated crop/livestock systems. The relative importance of crop residues increases with the aridity of the environment. Farmers in higher rainfall areas tend to concentrate on crop production, planting higher-yielding varieties and using more intensive management. Farmers in drier areas tend to derive a greater proportion of their income from livestock and are often adjacent to range areas with substantial livestock populations which may utilise crop residues on a seasonal basis. These generalisations interact with the availability of alternative feed resources and the overall balance of feed resources and livestock numbers. Crop residues are generally inadequate feed materials and their use in intercropping systems and with supplements needs consideration. However, the adequacy of crop residues as feed depends on the level of production desired, e.g. they may be adequate for non-pregnant, non- lactating animals but unsuitable for production. Better data are needed on the availability and use of crop residues. The major aim of crop selection programmes has been to increase grain yield. More experimental work is needed to determine the effect of this on residue quality. Work to date indicates a weakly negative association between grain yield and residue quality in some crops but the poor correlations indicate the possibility of 314 selecting varieties with both higher grain yield and good residue quality. Ideally, the digestibility of crop residues should be at least 50% but this may not be practicable for some crops. It would also simplify the task of the plant breeder if dual- purpose varieties could be identified i.e. those with good grain yields under favourable conditions but adequate residue quality in all locations. If this cannot be achieved, separate grain and fodder varieties should be identified. Digestibility and intake may be affected by particular chemicals, such as phenolics, and these need to be characterised. Chemical and biological indicators of crop residue value need to be improved and refined. 315 GROUP 5 Topic: Advantages and disadvantages of using crop residues for feeding ruminants in smallholder farming systems. Advantages o Higher whole -farm income o Higher return to cash and non-cash inputs o Provides an alternative source of feed to pastures and concentrates o Allows the maintenance of animals which would otherwise die reducing the farmers assets However, these advantages accrue only if feed resources are limiting. Disadvantages o Do not generally allow the use of genetically improved animals o Mineral deficiencies o Variable intake and digestibility o Harvesting, transport and storage problems o Legumes and/or chemical treatment may be necessary to make adequate use of crop residues. This may affect the availability of land and other resources necessary for food crops . o Alternative end uses of crop residues, including maintenance of soil organic matter, are important. Increased use of crop residues as feed could increase soil erosion or deforestation. 316 RECOMMENDATIONS General statement The international agricultural research centres (IARCs) and the national agricultural research systems (NARS) should recognise that farmers grow crops not only to feed themselves and their families but also to feed their animals. The rejection by farmers of high-yielding varieties because of their low straw yield or poor quality of straw or stover shows that attention must be paid to residue yield and quality in cereal crops. Specific recommendations 1. Survey data are needed on crop residue use by farmers . Such surveys should involve both agricultural economists and animal nutrition ists and aim particularly at understanding farmer perceptions. 2. Collaborative research should study the effects on stability of the farming system of alternative uses of crop residues and manure produced by ruminants fed on crop residues. This should involve crop and animal research institutes and include agroforestry input. 3. Chemical treatment of crop residues has limited applicability to animal production in tropical and sub- tropical countries. Emphasis should be transferred to exploiting genetic variation in crop residue quality. 4. The residues of existing varieties should be ranked in order of nutritive value, such rankings to include comparisons between years 317 and seasons from crops grown at a range of locations . In ranking crop residues, emphasis should be placed on biological methods, either in vitro or in sacco. This should be followed by voluntary intake and in vivo digestibility measurements and production trials. If near- infra-red reflectance is used to rapidly evaluate larger numbers of samples, it should be linked to biological measurements. Chemical and biological methods of selecting crop residues with higher nutritive value need to be improved and refined. The methods chosen need to be compatible with the objectives of the selection process and the type of crop residue. Variation in the nutritive value of crop residues arises from differences in morpho logical proportions, variation in cell wall digestibilities, differences in residual cell contents (particularly storage carbohydrates) and anti -nutritional factors, including phenolics. Research should be conducted to determine the relative importance of these variables in different crop species. Intake and digestibility of crop residues is affected by anti -nutritional factors, includ ing phenolics, which need to be characterised using techniques such as high-performance liquid chromatography. The existence of a negative correlation between grain yield and crop residue value has not been proved. Further studies are needed on this subject. 318 10. IARCs should evaluate the nutritive value of crop residues in advanced breeding lines or populations for all their major mandate crops . 11. IARCs should document the nutritive values of crop residues and forward this information along with information on grain yields to the NARSs. 12. NARSs should test the improved lines for their feeding values and supply data on performance to the relevant IARC for adjust ment of lines, where feasible, by plant breeders . 13. A link should be established, in countries where it does not exist, to rapidly pass the crops with improved feeding value to the small-scale farmers through extension staff. 14. Methods of storing crop residues need to be examined to prevent the effects of spoilage on deterioration of feeding value. With improved residues, which may be consumed in higher amounts, methods of assessing the quantities present in stacks would aid farmers in developing feeding strategies. 319 SESSION 5 RECOMMENDATIONS AND FUTURE PROSPECTS FOR PLANT BREEDING TO MAINTAIN OR IMPROVE THE NUTRITIVE VALUE OF CROP RESIDUES General discussion Onim: We need to arrive at a definition of what constitutes a crop residue. For instance, thinnings may be fed to animals before harvest. Kossila: Even materials such as potato peelings are, in my opinion, crop residues. Said: Byproducts are mostly fed with supple ments, such as urea/molasses, which may influence intake . Clearly the methodology for intake determination needs to be standardised. Berhane: I think that the general statement proposed for adoption by the meeting is too strongly worded. I do not believe that the CG centres should put more emphasis on crop residue value. Van Soest: The statement does not diminish the importance of grain production in any way. However, it may not be appropri ate to list priority crops for inves tigation of crop residues and there may be many important benefits from a particular variety before residue value should be considered. Gupta: Attempts should be made to find mor phological characteristics that are, associated with feeding values of crop residues . Jenkins: It would be useful to have correlated traits with which plant breeders could work. 321 Van Soest: Whatever selection methods are chosen it is important that they are compatible with the objectives of the work. Gupta: If the traits related to nutritive value were known even as many as 10,000 samples would not be too large a number in a plant breeding programme . I agree that one should avoid screening entire gene banks . Jenkins: I believe it would be unwise to be specific on the scale of any evaluation programme . Van Soest: It is usually necessary to use plant criteria including grain yield to narrow down the number of entries that can be fully evaluated in the labora tory to about 200. Subsequently resi dues from no more than 12 varieties could be subjected to full animal evaluation. In addition one could include a few parent lines with prom ising value. Perhaps I should also mention that work on an European Com munity project being conducted in the Netherlands has shown that varieties of maize grown in Europe have digest ibilities of residues 10 units higher than those grown in the USA and this does not appear to be an environmental effect. Berhane : In my previous comments I was not questioning the practical value of investigating variation in crop residue quality. However I would not see this as a primary responsibility of the CG centres , which should concentrate on grain yield and grain quality. To bring in crop residue 322 Fussell : Witcombe : Little: Onim: McAllan: Fussell ; Reed: value as an index of selection would not serve the immediate mandate of CIMMYT to increase yields of wheat and maize . The question of whether crop residues are important needs to be put to the ultimate user of new varieties, the farmer. More information is needed as to what is happening at the farmer level, through more feedback from extension services. Ground- level surveys are needed, involving cooperation between econo mists and animal nutritionists, in order to obtain farmers' perceptions regarding the acceptability of new varieties. This should form a major recommendation . We need to know the base-line consid erations of farmers concerning crop residues . There appears to be a need to intro duce animal nutritionists at crop research centres . It would concern me that the number of materials to be evaluated may exceed the capacity of animal nutrition facilities. Should animal nutrition ists be in a monitoring or collabora tive role? I would suggest looking at current varieties first. For example in West Africa only five or six millet varieties would need to be fully evaluated. Perhaps we are putting too much emphasis on the need for farmer surveys. For instance we already know that the digestibility of barley straw 323 in the Ethiopian highlands is 55% whereas in Europe it is only 35%. Information is already available for groundnut residues in Senegal. I consider it more important to deal with the effects of crop management on residue values so that they are at least capable of maintaining the animals . Little: Emphasis needs to be placed on finding an appropriate method of evaluation for particular crops. Subsequently such tests could then be run by laboratory technicians. Van Soest: I think that one will need more than one parameter to effectively identify varieties with superior crop residue value. The use of plant criteria followed by investigations of crop residue value would seem to be the best means of tackling the large number of entries available. It would be useful to have contribu tions from national programme repre sentatives . In Ethiopia I consider that we must continue to give priority to grain production, to consider residue value may be a luxury. Yet this workshop has been an eye-opener and, provided progress is maintained on other aspects of plant breeding, it may well be possible to put together programmes which take into account the nutri tional aspects of crop residues. McDowell: At a recent Centres week, representa tives from Africa expressed a prefer ence for hydrids rather than selected varieties. This may relate to yield Jenkins : Kebede : 324 and quality of residues. For instance in maize stover yields of hybrid varieties were superior to open pollinated varieties. Witcombe: It is probable that the choice is dictated by the primary economic factors of seed production. I do not think it likely that the quality of stover differs between hybrids and open pollinated varieties. Pearce : The remaining question is the matter of collaboration between animal nutritionist and plant breeders. Animal nutritionists can distinguish between a number of straws with varying nutritional quality but the input of the plant breeder is needed to tell the animal nutritionist what is practically feasible. McDowell: The question of the feeding value of crop residues is one that should concern all plant breeders in national programmes as well as the internation al centres. Jenkins: The workshop has been most stimulating and may be the first time that plant breeders and animal nutritionists have met to consider the question of crop residues. It is clear that in many situations farmers are interested in the value of these residues. I am sure we would all like to thank ILCA for organising this workshop and Capper and Reed for the original concept. 325 LIST OF PARTICIPANTS LIST OF PARTICIPANTS Dr. Geoff PEARCE School of Agriculture and Forestry University of Melbourne Parkville Victoria 3052 AUSTRALIA Dr. YILMA Kebede Institute of Agricultural Research Melkasa Nazareth ETHIOPIA Dr. Vappu L. KOSSILA Institute of Agricultural Research SF-31600 Jokioinen FINLAND Dr. Moses ONIM Small Ruminant Collaborative Support Programme P.O. Box 252 Maseno KENYA Mr. Abdool A. B00D00 Ministry of Agriculture and Natural Resources Division of Animal Production Reduit MAURITIUS Dr. Abdalla B. El AHMADI Plant Breeding Station Gezira Research Station P.O. Box 126 Wad Medani SUDAN 329 Mr. Milton MKHABELA University of Swaziland Luyengo Campus P.O. Luyengo Luyengo SWAZILAND Dr. Peter UDEN Department of Animal Husbandry Swedish University of Agricultural Sciences S-750 07 Uppsala 7 SWEDEN Mr. Rashidi KIDUNDA Sokoine University of Agriculture P.O. Box 3004 Morogoro TANZANIA Mr. R.N. MERU Ministry of Agriculture and Livestock Development P.O. Box 51 Mpwapwa TANZANIA Mr. Ali 0. ABOUD University of Reading Department of Agriculture Early Gate Reading RG6 2AT UNITED KINGDOM Mr. Brian S. CAPPER Overseas Development and Natural Resources Institute 56/62 Grays Inn Road London WC1X 8LU UNITED KINGDOM 330 Ms. Frances HERBERT Wye College University of London Wye , Ashford Kent TN25 5AH UNITED KINGDOM Mr. Graham JENKINS Plant Breeding Institute Maris Lane Trumpington, Cambridge UNITED KINGDOM Dr. Alexander B. McALLAN Animal and Grassland Research Station Hurley, Maidenhead Berkshire SL6 5LR UNITED KINGDOM Dr. Irene MUELLER-HARVEY Animal and Grassland Research Station Hurley, Maidenhead Berkshire SL6 5LR UNITED KINGDOM Dr. Robert E. 0RSKOV Rowett Research Institute Greenburn Road Bucksburn Aberdeen AB2 9SB UNITED KINGDOM Prof. Peter J. VAN SOEST Department of Animal Science Cornell University Morisson Hall Ithaca NY 14853 USA 331 Prof. Robert E. McDOWELL Department of Animal Science North Carolina State University P.O. Box 7621 Raleigh NC 27695 USA INTERNATIONAL CENTRES Centro Internacional de Agricultura Tropical (CIAT) Dr. Richard KIRKBY CIAT c/o ILCA P.O. Box 5689 Addis Ababa Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT) Dr. BERHANE Gebrekidan CIMMYT East African Regional Maize Program P.O. Box 25171, Nairobi KENYA Dr. Maarten van GINKEL CIMMYT c/o ILCA, P.O. Box 5689 Addis Ababa ETHIOPIA Dr. Douglas TANNER CIMMYT c/o ILCA, P.O. Box 5689 Addis Ababa ETHIOPIA 332 International Center for Agricultural Research in the Dry Areas (ICARDA) Dr. Euan F. THOMSON ICARDA P.O. Box 5466 Aleppo SYRIA Dr. Thomas L. NORDBLOM ICARDA P.O. Box 5466 Aleppo SYRIA International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) Dr. John R. WITCOMBE ICRISAT Patancheru Andrha Pradesh 502 324 INDIA Dr. Leslie K. FUSSELL ICRISAT- -Centre Sahelien B.P. 12404 Niamey NIGER Dr. Subhash C. GUPTA SADCC/ICRISAT Sorghum/Millet Improvement Programme P.O. Box 776 Buiawayo ZIMBABWE 333 International Rice Research Institute (IRRI) Dr. Gurdev S. KHUSH IRRI P.O. Box 933 Manila THE PHILIPPINES ILCA PARTICIPANTS Dr. John WALSH Director General Dr. Ishanoul HAQUE Head of Soil Science Dr. Kurt PETERS Deputy Director General (Research) Dr. Cherrnor S. KAMARA Visiting Scientist Dr. Douglas LITTLE Head of Nutrition Dr. John McINTIRE Economist Dr. Jess REED Animal Nutritionist (Scientific coordinator of the workshop) Dr. Samuel JUTZI Forage Agronomist Dr. Abdullah N. SAID ARNAB Coordinator Mr. ABATE Tedla Forage Agronomist Mr. YILMA B. Asfaw Adminis trat ive coordinator of the workshop Mr. Paul J.H. NEATE Science Writer (Workshop editor) 334 Printed at ILCA, Addis Ababa, Ethiopia