Sustainable management of globally significant endemic ruminant livestock in West Africa: Estimate of livestock demographic parameters in Senegal RESEARCH PROGRAM ON Livestock and Fish ILRI R esearch Repo rt 2 9 IL R I R E S E A R C H R E P O R T 29 ISBN 92–9146–277–2 CGIAR is a global agricultural research partnership for a food-secure future. Its science is carried out by15 research centres that are members of the CGIAR Consortium in collaboration with hundreds of partner organizations. cgiar.org The International Livestock Research Institute (ILRI) works to enhance the roles livestock play in pathways out of poverty in developing countries. ILRI is a member of the CGIAR Consortium, a global research partnership of 15 centres working with many partners for a food-secure future. ILRI has two main campuses in East Africa and other hubs in East, West and southern Africa and South, Southeast and East Asia. ilri.org Projet Regional de Gestion Durable du Betail Ruminant Endemique (PROGEBE) (Sustainable Management of Globally Significant Endemic Ruminant Livestock in West Africa) Sustainable management of globally significant endemic ruminant livestock in West Africa: Estimate of livestock demographic parameters in Senegal Maria Ejlertsen, Jane Poole and Karen Marshall* * Corresponding author: k.marshall@cgiar.org © 2012 International Livestock Research Institute (ILRI) This publication is copyrighted by the International Livestock Research Institute (ILRI). It is licensed for use under the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License. To view this license, visit http://creativecommons.org/licenses/by-nc- sa/3.0/. 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The parts used must not misrepresent the meaning of the publication. ILRI would appreciate being sent a copy of any materials in which text, photos etc. have been used. Editing, design and layout—ILRI Editorial and Publishing Services, Addis Ababa, Ethiopia. Cover photo credit: ILRI/Stevie Mann ISBN 92–9146–277–2 Citation: Ejlertsen, M., Poole, J. and Marshall, K. 2012. Sustainable management of globally significant endemic ruminant livestock in West Africa: Estimate of livestock demographic parameters in Senegal. ILRI Research Report 29. Nairobi: International Livestock Research Institute. International Livestock Research Institute P O Box 30709, Nairobi 00100, Kenya Phone + 254 20 422 3000 Email ILRI-Kenya@cgiar.org P O Box 5689, Addis Ababa, Ethiopia Phone + 251 11 617 2000 Email ILRI-Ethiopia@cgiar.org Offices in: Bamako . Beijing . Delhi Hanoi . Hyderabad . Ibadan . Kampala . Maputo . Vientian e ilri.org iiiSustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Contents Tables v Figures vi Acronyms vii Acknowledgements viii Executive summary ix 1 Introduction 1 2 Methodology 3 2.1 Overview of survey methodology and demographic parameters estimated 3 2.2 Cattle survey sample 6 2.3 Sheep survey sample 6 2.4 Goat survey sample 7 3 Cattle results 9 3.1 Herd sizes and structure 9 3.2 Reproduction 10 3.3 Natural mortality 12 3.4 Offtake and intake 13 4 Sheep results 15 4.1 Flock sizes and structure 15 4.2 Reproduction 16 4.3 Natural mortality 18 4.4 Offtake and intake 19 5 Goat results 21 5.1 Herd sizes and structure 21 5.2 Reproduction 22 iv Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal 5.3 Natural mortality 24 5.4 Offtake and intake 25 6 Discussion 27 6.1 Key demographic parameters 27 6.2 Findings on existing breeding strategies and their implications 28 6.3 Considerations for use of survey data 29 7 Conclusion and summary of main recommendations 30 References 31 Appendix 1: Illustrative example of instantaneous hazard rates in relation to this survey 33 vSustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Tables Table 1. Data recorded for the 12 month retrospective survey 4 Table 2. Demographic parameters estimated for the 12 months retrospective survey 5 Table 3. Various estimates of the annual parturition rates for female cattle 11 Table 4. Estimates of abortion for cattle 12 Table 5. Annual offtake rates (standard errors) for cattle, for different offtake events 12 Table 6. Annual intake rates for cattle, for different intake events 14 Table 7. Net offtake rates for cattle, as well as the underlying offtake and intake rates 14 Table 8. Various estimates of the annual parturition rates for female sheep 17 Table 9. Estimates of abortion rates for sheep (standard errors) 18 Table 10. Annual offtake rates (standard errors) for sheep, for different offtake events 19 Table 11. Annual intake rates (standard errors) for sheep, for different intake events 19 Table 12. Net offtake rates for sheep, as well as the underlying offtake and intake rates (standard errors) 20 Table 13. Various estimates of the annual parturition rates for female goat 23 Table 14. Estimates of abortion rates for goats (standard errors) 24 Table 15. Annual offtake rates (standard errors) for goats, for different offtake events 25 Table 16. Annual intake rates (standard errors) for goats, for different intake events 25 Table 17. Net offtake rates for goats, as well as the underlying offtake and intake rates (standard errors) 26 vi Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Figures Figure 1. Interviewees’ perception of 12 month study period for cattle herds in the three sites 6 Figure 2. Interviewees’ perception of 12 month study period for sheep flocks in the three sites 7 Figure 3. Interviewees’ perception of 12 month study period for goat herds in the three sites 8 Figure 4. Distribution of cattle herd sizes 9 Figure 5. Age-by-sex structure in the surveyed cattle herds 10 Figure 6. Parity in relation to age class for cattle 10 Figure 7. Annual parturition rates of female cattle, with 95% confidence intervals indicated 11 Figure 8. Annual mortality rates for natural death of cattle 13 Figure 9. Distribution of sheep flock size 15 Figure 10. Age-by-sex structure in the surveyed sheep flocks for females (F) and males (M) 16 Figure 11. Parity in relation to age class for sheep 16 Figure 12. Annual parturition rates of female sheep, with 95% confidence intervals indicated 17 Figure 13. Annual mortality rates for natural death of sheep 18 Figure 14. Distribution of goat herd size 21 Figure 15. Age-by-sex structure in the surveyed goat herds 22 Figure 16. Parity in relation to age class for goats 22 Figure 17. Annual parturition rates of female goat, with 95% confidence intervals indicated 23 Figure 18. Annual mortality rates for natural death of goats 24 viiSustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Acronyms ERL Endemic Ruminant Livestock NARS National Agricultural Research System PPR Peste des Petits Ruminants PRA Participatory Rural Appraisal PROGEBE Projet Régional de Gestion Durable du Bétail Ruminant Endémique (Sustainable Management of Globally Significant Endemic Ruminant Livestock in West Africa) WAD West African Dwarf viii Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Acknowledgements We would very much like to thank the farmers that were interviewed for this survey, for their time and patience. We would also like to thank members of the PROGEBE National and Site Coordination Units in Senegal, the enumerator teams and data-entry personnel, the drivers, and other field staff for their support. We are also very grateful to Matthieu Lesnoff, the developer of this survey, for initial training and invaluable assistance in relation to data analysis and interpretation. Data were collected as part of the project ‘Regional Project on Sustainable Management of Endemic Ruminant Livestock in West Africa’ (PROGEBE: see http://www.progebe.net/). The project is funded by two major financers, the Global Environment Fund (GEF) and the African Development Bank (AfDB), with support from the governments of the participating countries (The Gambia, Guinea, Mali and Senegal), and is implemented by the United Nations Office for Project Services (UNOPS) and the United Nations Development Programme (UNDP). ixSustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Executive summary Introduction This report describes the results of a 12-month retrospective survey for estimating livestock demographic parameters of endemic ruminant livestock (ERL) kept by smallholders in selected sites in Senegal. The demographic parameters estimated included natural rates, such as parturition, abortion and mortality rates, as well as management rates, such as offtake and intake rates. The survey was carried out as one of several baseline surveys under the PROGEBE-Senegal project. At the onset of the survey, it was expected that the output (demographic parameter estimates) would serve the following functions: a) as an information source (to be combined with other information sources) for prioritizing project interventions, b) for quantitative comparison of the demographic parameters between ERL and non-ERL, and c) to provide indications of the baseline status of livestock demographic parameters, which in combination with other baseline data and consideration for year effect can be used for evaluating the impact of project interventions. However, as there were very few non-ERL within the surveyed sites, quantitative comparison of demographic parameters between ERL and non-ERL has not been possible. Methodology The methodology utilized was a 12-month retrospective survey, as described in full in Lesnoff et al. (2010a). The survey was carried out between the 4th of December 2009 and the 22 nd of January 2010, and thus encompasses the 12 month period prior to this. Suitable herds/flocks for enumeration were first identified within the project sites. These were considered those of size 5 to 30 animals (including juveniles) for a single household owned herd/flock, and 15 to 50 animals (including juveniles) for a multiple household owned herd/flock (though on occasion smaller or larger herds/flocks were surveyed). A trained enumerator then interviewed the farmer in relation to their herd/flock, in the presence of the animals. These animals were enumerated exhaustively for a number of basic data (such as breed, sex, age, parity etc.). The interviewee was also asked to recall all demographic events (such as births, deaths, slaughters, sales, purchases) that have occurred in the last 12 months. From the data collected, two types of demographic parameters were estimated (Lesnoff et al. 2010a): variables describing the state of the herd/flock at the time of survey (such as herd size, sex by age structure), and annual demographic rates (including natural rates, such as parturition, abortion and mortality rates, as well as management rates, such as offtake and intake rates). x Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal The demographic parameters referred to as a rate (for example mortality rate, parturition rate) are instantaneous hazard rates. These are estimated as the number of events (e.g. number of mortalities) that have occurred in the last 12 months, divided by the total ‘time at risk’ (time spent by animals in the category over the last 12 months). It should be noted that the demographic parameters were calculated for pure-breed ERL only (due to the low number of non-ERL in the data). Further the estimated parameters should be considered approximate and interpreted with caution, due to several reasons (such as being based on recall) as discussed further in the main report. Sample characteristics The survey was carried out in three sites in Senegal, namely Bandafassy, Oussadou and Tenghory (see ILRI 2011 for more details). In total, 100 cattle herds were surveyed; 36 from Bandafassy, 34 from Oussadou, and 30 from Tenghory. The total number of animals within these herds at the time of survey was 1849, of which 1847 (99.9%) were pure-bred N’Dama. All interviewees, but one, were male. Sixty-seven sheep flocks were surveyed in total; 32 from Bandafassy, 29 from Oussadou, and 6 from Tenghory. The total number of animals within these flocks at the time of survey was 581, of which all were pure-bred Djallonke. Ninety-four per cent of interviewees were male. Eighty-three goat herds were surveyed in total, 32 from Bandafassy, 28 from Oussadou, and 23 from Tenghory. The total number of animals within these herds at the time of survey was 748, of which all were pure-bred West African Dwarf (WAD). Ninety-five per cent of interviewees were male. Interviewees’ perception of 12 month study period The 12-month period prior to the survey was generally rated as an average year according to the perception of the interviewees, across sites and species. Key results Herd size and structure The mean herd size for cattle was 18 animals, with an overall herd structure of 15% calves ( ≤1 year), 38% subadults (>1 to ≤4 years) and 37% adult females and 10% adult males (>4 years). For sheep the mean flock size was nine animals with an overall flock structure of 48% lamb ( ≤1 year), 44% adult females and 8% adult males (>1 year). Finally, for goats the mean herd size was nine animals, with an overall herd structure of 54% kids ( ≤1 year), 40% adult females and 6% adult males (>1 year). All three species had animals not born within the herd/flock. However, the proportion of introduced animals was low (1–4%) for all species/age/sex groups except for female sheep and goat >1 year of age (21 and 10%, respectively). Reproduction Some variation in the age at first calving for cattle was found (generally four to six years), while the age at first lambing/kidding for small ruminants generally was around one year of age. The parturition interval was high for all species, namely 2.3 for all female cattle ≤4 years and 1.3 for all female sheep and goats ≤3 years. The annual abortion rate was low for cattle (0.01), reasonable for goats (0.04) and slightly high for sheep (0.06). The stillbirth rate, prolificacy rates and fecundity rates were not possible to estimate due to low number of respondents. xiSustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Natural mortality The mortality rates were found to be moderately high for female sheep ≤1 year of age (0.15) as well as male goats >1 year of age (0.15), and moderate for male sheep of all ages (0.07). Overall, estimated losses for a typical herd/flock of 18 cattle, 9 sheep or 9 goats (assuming constant herd/flock size over the year) were 0.4, 0.5 and 0.5 animals per annum, respectively. Offtake and intake The overall annual offtake rate was 0.08 for cattle, 0.20 for sheep and 0.14 for goats. Thus for a typical herd/flock of 18 cattle, 9 sheep or 9 goats (assuming constant herd/flock size over the year) 1.4, 1.8 and 1.3 animals would be expected to exit via offtake (rather than death) annually. The highest single event offtake rate was sale, followed by slaughter. The annual intake rate was 0.02 for cattle and sheep and 0.03 for goats. Thus for a typical herd/flock of 18 cattle, 9 sheep or 9 goats (assuming constant herd/flock size over the year), 0.4, 0.3 and 0.3 animals, respectively, are expected to enter the herd/flock (by means other than birth) annually. The only type of intake was purchase/barter for all species. Mainly animals >1 year of age were purchased. The overall net offtake rates per annum were 0.06 for cattle, 0.17 for sheep and 0.11 for goats. Conclusions and key recommendations The findings of this survey clearly indicate that N’Dama cattle, Djallonke sheep, and WAD goat are the prominent breeds in the PROGEBE-Senegal project areas and suggests that some level of controlled breeding seems to be applied in most herds/flocks, primarily through sire selection (although these may or may not be implemented with a specific breeding objective in mind). There seem to be a considerable scope for improvement of especially reproductive demographic parameters through improved herd/flock management in the short term, and breeding strategies in the long term. Specifically, it can be recommended that PROGEBE consider/prioritize the following issues for future project activities or interventions: Interventions towards lowering the natural mortality. In the short to medium term (next few to 20 years) this • should mainly be through changes to management practices. The results from the PROGEBE Senegal household survey (ILRI 2011) suggest that the main areas of intervention should be in relation to diseases and feed resources. However, any scheme of interventions should be based on local conditions and further investigations are required in this regard. In the much longer term (20 to 50 years) it may be possible to reduce mortality by genetically improving the animals through a breeding program. Interventions to improve reproductive parameters should be prioritized, namely, age at first parturition, • parturition interval and abortion rates. Again, this should mainly be through changes in management practices in the short-term, such as improved feeding, while in the longer term these parameters could potentially be improved through genetic improvement. Capacity building programs to improve awareness of traditional and alternate management and breeding practices • and the effect these have on livestock production and productivity. A modelling study utilizing the demographic parameters estimated here, combined with other data from the • household survey, livestock census and literature to determine the expected impact of potential PROGEBE interventions (such as improved health-care, feeding and/or animal genetic improvement) on livestock production over different time horizons. 1Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal 1 Introduction Livestock play a central role in rural development in West Africa (Agyemang 2005). However, traditional livestock systems are in general characterized by high mortality rates, low reproductive rates and low offtake rates (Otte and Chilonda 2002). Furthermore, the presence of trypanosome-infected tsetse flies in the subhumid and humid areas seriously affects the potential for livestock production (Murray and Trail 1984; Snow et al. 1996; Osaer et al. 1999). Endemic ruminant livestock (ERL) such as N’Dama cattle, Djallonke sheep and West African Dwarf (WAD) goats are, however, highly adapted to the local environmental conditions and are able to survive and remain productive in tsetse infested areas with minimal inputs where other breeds succumb (Murray and Trail 1984; Wilson 1991; Snow et al. 1996; Osaer et al. 1999). Conservation and improvement of these breeds therefore have the potential to unlock the role of livestock in improving the livelihoods of livestock keepers in West Africa. The ‘Sustainable Management of Globally Significant Endemic Ruminant Livestock in West Africa’ (PROGEBE) project aims at developing and implementing models for community-based conservation and management of critical habitats for three endemic ruminant livestock (ERL) species (namely, N’Dama cattle, Djallonke sheep and WAD goats), and to demonstrate strategies for preserving the unique genetic trait/habitat complexes that are of global importance. Specifically, the objectives of the project are: 1) to ensure sustainable populations of targeted ERL breeds in four West African countries; and 2) to contribute to food security improvement and poverty reduction. These objectives will be accomplished through reaching the following outcomes: i) conserving ERL genetic traits and improving their productivity; ii) facilitating improved market development and incentives for ERL and their products; iii) promoting sustainable management of natural resources for ERL; iv) facilitating the implementation of policies, legal and institutional frameworks favourable to ERL development; and v) improve cooperation, knowledge management and information sharing (UNDP 2007). In order to characterize the existing ERL production and management system, as well as other key indicators relevant to the five strategic intervention areas, a number of baseline surveys were carried out in the three project sites in Senegal. These included a participatory rural appraisal (PRA) survey, a household questionnaire survey, a market actor survey and a retrospective survey of livestock demographic parameters. This report describes the results of the 12-month retrospective survey for estimating livestock demographic parameters of endemic ruminant livestock (ERL) kept in mixed crop–livestock systems in Senegal. These parameters have to some extent been reported in the literature for cattle (Agyemang et al. 1997; Otte and Chilonda 2002; Ba et al. 2011), sheep (Wilson 1991; Lesnoff 1999; Otte and Chilonda 2002) and goats (Wilson 1991; Ba et al. 1996; Otte and Chilonda 2002). However, the data are typically 10–40 years old and has limitations in terms of livestock species and breeds, farming system or country/region. Hence, this survey was carried out to collect up-to- date, site and breed specific data on livestock demographic parameters in the PROGEBE-Senegal project sites. Three main survey approaches are used in practice for collecting data on livestock demographic parameters in smallholder systems in the developing world. These are individual animal follow-up, herd follow up and cross-sectional retrospective surveys (Lesnoff et al. 2009). The retrospective survey is based on farmer interviews and their recall of past herd demographics. Compared to the other two methods it has the advantage of quick results and being 2 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal relatively low cost. The main drawback is that the method relies on farmers’ recall of past event and therefore will not be as accurate at the two other approaches. The 12MO (12 months) retrospective survey is a methodology designed to provide a standardized methodology for estimating livestock demographic parameters, which is affordable and easily implementable in the field in order to be easily transferable to local structures (NARS, NGOs etc.) (Lesnoff et al. 2009). Being based on farmers’ recall of the past 12 months, the survey is sensitive to between year variation, which can be considerable (Lesnoff 1999). This survey methodology was, however, still found to be the most suitable for the purpose, due to the reasons given above and since no up-to-date site and species/breed specific data were available. The results of the survey should be interpreted with consideration of the interviewees’ perception of the 12 month study period and cannot be considered as averages over years. They can, however, provide a useful and site/ breed specific estimation of the productivity of livestock herds in the year prior to the survey. The advantages and disadvantages of the 12MO survey methodology are further discussed in the following section. The specific objectives of the survey were as follows: i. To serve as an information source that, combined with other information sources, can be used for prioritizing project interventions, ii. To enable quantitative comparison of the demographic parameters between ERL and non-ERL, and iii. To provide indication of the status of livestock demographic parameters in the project sites that, in combination with other baseline data and with consideration of year effect, can be used for evaluating the impact of project interventions. However, as there were very few non-ERL in the surveyed sites, the second objective could not be fulfilled. The report first describes the methodology used for the survey, as well as the sample surveyed for each of the three species (cattle, sheep and goat) (Section 2). Hereafter the results of the survey are presented by species (Sections 3, 4 and 5, respectively), followed by an overall discussion (Section 6). Finally, a conclusion and summary of recommendations for future PROGEBE interventions are given in Section 7. 3Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal 2 Methodology 2.1 Overview of survey methodology and demographic parameters estimated The methodology utilized was a 12-month retrospective survey, as described in full in Lesnoff et al. (2010a). The survey was carried out between the 4th of December 2009 and the 22 nd of January 2010, and thus encompasses the 12 month period prior to this. The survey was carried out as follows. Suitable herds/flocks for enumeration were first identified within the project sites. These were considered those of size 5 to 30 animals (including juveniles) for a single household owned herd/ flock, and 15 to 50 animals (including juveniles) for a multiple household owned herd/flock (though on occasion smaller or larger herds/flocks were surveyed). These herd/flock sizes were chosen as a compromise between fully representative of all herd/flock sizes, and practical issues related to survey time (the overhead associated with surveying smaller herd/flocks was considered too great, and it was too time-consuming to survey larger herd/flocks). The results of the PROGEBE Senegal household survey showed that 62, 58 and 58% of households owning cattle, sheep and goats, respectively, owned 5–30 animals, while 36, 40 and 21%, respectively, owned 1–4 animals. Difference in demographic parameters may exist between these two major groups of households, which should be considered when interpreting the results. Ba et al. (2011) did not find a significant difference in mortality and offtake rates between different herd sizes for cattle in mixed crop–livestock systems in Southern Mali. The main differences found were that herds of 1–5 cows had significantly a higher parturition rate compared to herds of 6–19 and ≥20 cows, as well as significantly higher intake of subadult and adult animals. A trained enumerator then interviewed the farmer in relation to their herd/flock, in the presence of the animals. These animals were enumerated exhaustively for a number of basic data (such as breed, sex, age, parity etc.). The interviewee was also asked to recall all demographic events (such as births, deaths, slaughters, sales, purchases) that have occurred in the last 12 months. A full list of the data recorded is given in Table 1. From this data two types of demographic parameters were estimated (Lesnoff et al. 2010a): 1. variables describing the state of the herd/flock at the time of survey (such as herd size, sex by age structure); 2. annual demographic rates (including natural rates, such as parturition, abortion and mortality rates, as well as management rates, such as offtake and intake rates). 4 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Table 1. Data recorded for the 12 month retrospective survey Level Data For each survey Generic: survey date, survey location (site, village and GPS coordinates) Interviewee: name, gender, type (household head, other household member, herder, or other), livestock owner (yes, no) Seasonal effect over the last 12 months compared to the previous 5 years (choices of ‘much worse than average’, ‘somewhat worse than average’, ‘average’, ‘somewhat better than average’, ‘much better than average’, with respective scores of 1, 2, 3, 4 and 5 Total number of households with animals within the herd/flock For each animal present in the herd/ flock at the time of survey Breed or breed-cross: based on phenotype, and as jointly agreed by the interviewee and enumerator Sex Born in herd Born from AI Age: as age class, where age class 0 corresponds to animals 0 to ≤1 year of age, age class 1 corresponds to animals >1 and ≤2 years of age etc. For each female present in the herd/ flock at the time of survey Number of lifetime parturitions (where a parturition is defined as the process of giving birth) Number of parturitions over the last 12 months For each parturition over the last 12 months the number of offspring born alive For each parturition over the last 12 months the number of offspring stillborn Number of lifetime abortions Number of abortions over the last 12 months For each animal that has entered the herd over the last 12 months Breed or breed cross (as above) Sex Age (as above) Type of entry: purchase or barter; arrival in loan or contract; returned from loan or contract; gift, inheritance of dowry For each animal that has exited the herd over the last 12 months Breed of breed cross (as above) Sex Age (as above) Type of exit: natural death; slaughter; sale or barter; departure in loan or contract; sending back from loan or contract; gift or dowry; withdrawal or theft Type of slaughter or sale: ordinary; emergency due to disease; emergency due to lack of feed; emergency due to traumatism A full list of demographic parameters is given in Table 2. The stillbirth rate, prolificacy rates and fecundity rates are not included in this report, since the data used for estimation of these rates were only collected for a small number of animals (n = 4–28, depending on species and rate). A number of demographic parameters in Table 2 (i.e. abortion, parturition, mortality, offtake and intake) are given as an instantaneous hazard rate (h). The instantaneous hazard rate was estimated for a particular category of animals and event (e.g. males over one year of age and offtake via slaughter) as: h = m/T where m is the number of events that have taken place in the last 12 months, and T is the total ‘time at risk’ (time spent by animals in the category over the last 12 months). 5Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Table 2. Demographic parameters estimated for the 12 months retrospective survey1 Natural rates Abortion rate Annual instantaneous hazard rate of abortion (expected number of abortions per female when spending all the year in the herd; an abortion is a gestation that has not reached its term). Also calculated over the complete reproductive female histories (as the slope of the regression line fitted between ages and parities of the females present in the herd) Parturition rate Annual instantaneous hazard rate of parturition (expected number of parturitions per female when spending all the year in the herd). Also calculated over the complete reproductive female histories (as the slope of the regression line fitted between ages and parities of the females present in the herd) Prolificacy rate Average number of offspring (stillborn or born alive) per parturition Stillbirth rate Probability that an offspring is a stillborn (stillbirth is not included in the mortality rate, which only concerns animals born alive) Mortality rates Management rate Annual instantaneous hazard rate of natural death (natural death refers to all types of death except slaughtering) Offtake rate Annual instantaneous hazard rate of offtake (slaughtering, sales, loans, gifts etc.) Intake rate Annual instantaneous hazard rate of intake (purchases, loans, gifts etc.) Additional demographic rates derived from the basic annual demographic rates Net prolificacy rate Average number of offspring born alive per parturition, calculated directly or by: Prolificacy rate * (1-stillbirth rate) Fecundity rate Average number of offspring (born alive or stillborn) per reproductive female and year, calculated directly or by: Parturition rate * Prolificacy rate Net fecundity rate Average number of offspring born alive per reproductive female and year, calculated directly or by: Parturition rate * Net prolificacy rate 1. Taken from Lesnoff et al. (2010a). T is approximated by averaging the estimated number of animals in that category 12 months ago ( n t – 1 ), and the current number of animals in that category (n t ). n t – 1 for a particular age class (i) is calculated as: n t–i, i = n t, i+1 – ((m ent, i – m exi, i )/2) – ((m ent, i+1 – m exi, i+1 )/2) where m ent and m exi are entries and exists into age class i in the last 12 months, respectively. n t, i is known from the data. Note that calculation of T via this method assumes a uniform distribution of events (mortalities, number of animals entering the herd etc.) over the 12 months. If this assumption does not hold and there is a non-uniform event rate T will be biased: if an intensive event rate occurs close to the beginning of the year T will be over-estimated, and if an intensive event rate occurs close to the end of the year T will be under-estimated. In practice this assumption cannot be expected to be met fully. It has, however, been shown that this method of estimating T is less sensitive to herd size variations over the year than other methods (Lesnoff 2008). For further details on the calculation of instantaneous hazard rates, see Lesnoff et al. (2010a) and for an illustrative example see Appendix 1. Furthermore, it should be noted that the data produced using this methodology should only be considered approximate and should be interpreted with caution for several reasons. Firstly, the data is based on a memory of events for the 12 month period preceding the time of survey, and thus is likely to contain a certain level of error, which could bias the results. Secondly, an underlying assumption for the annual hazard rates is that there is a uniform distribution of demographic events over time, with violation of this assumption again biasing the results. In particular, this may apply to adult male small ruminants as these are often slaughtered or sold during a short time period (e.g. Tabaski) but also to whole herds/flocks during the occurrence of seasonal disease outbreaks, such as PPR for sheep and goats. Thirdly, herds and flocks were selected based on a specific size range, meaning that results are less applicable to herds/flock smaller or larger than that targeted here. Finally, the results relate to the specific environmental conditions of the 12-month period surveyed, rather than being an average over many years. The best option for validation of the demographic parameters presented here, if required, is a long-term longitudinal survey. All analyses, except interviewees’ perception of 12 month study period, were performed combining data over sites. 6 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal 2.2 Cattle survey sample A total of 100 herds were surveyed; 36 from Bandafassy, 34 from Oussadou, and 30 from Tenghory. All herds were single-household owned. The total number of animals within these herds at the time of survey was 1849. Of these, 1847 (99.9%) were pure-bred N’Dama. The final data-set used for the analysis comprised of 1828 animals (with 2 animals excluded for not being pure-bred N’Dama, and a further 19 animals excluded for missing data). In addition, there were a total of 35 entries and 170 exits of pure-bred N’Dama recorded. All but one of the interviewees were male (99%), with 99% of interviewees being household heads and 1% ‘other household member’. All household heads were livestock owners, while the one ‘other [male] household member’ was not the owner of the livestock. Interviewees’ perception of 12 month study period The distribution of scores for the interviewees’ perception of the 12 month study period is given in Figure 1. Overall, the great majority of interviewees perceived the year to be an average year. In Bandafassy, 3% rated the year as ‘much worse than average’, 89% as average, and 8% as ‘better than average’. In Oussadou and Tenghory, 94 and 90%, respectively, rated the year as average, while 6 and 10%, respectively, rated the year as ‘much worse than average’. Figure 1. Interviewees’ perception of 12 month study period for cattle herds in the three sites Much worse than average Worse than average Average Better than average Site 0 20 40 60 80 10 0 Bandafassy Ou sadou Tenghory Percent 2.3 Sheep survey sample In total 67 flocks were surveyed; 32 from Bandafassy, 29 from Oussadou, and 6 from Tenghory. All flocks were single-household owned. The total number of animals within these flocks at the time of survey was 581, all of which were pure-bred Djallonke. The final data-set used for the analysis comprised 578 animals (with 3 animals excluded for missing data). In addition, there were a total of 19 entries and 144 exits recorded of pure-bred Djallonke. 7Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Ninety-four per cent of the interviewees were male, with 97% of interviewees being a household head and 3% (2) ‘other household member’. All household heads were livestock owners, while one ‘other [female] household member’ was a livestock owner and the other ‘other [female] household member’ was not. Interviewees’ perception of 12 month study period The distribution of scores for the interviewees’ perception of the 12 month study period in each site is given in Figure 2. Overall, the great majority of interviewees perceived the year as average. All interviewees in Figure 2. Interviewees’ perception of 12 month study period for sheep flocks in the three sites 0 20 40 60 80 100 Bandafassy Oussadou Tenghory Site Average Much better than averageBetter than average Percent Oussadou and Tenghory rated the year as average, while in Bandafassy 94% rated the year as average, 3% rated the year as better than average, and 3% as much better than average. 2.4 Goat survey sample A total of 83 herds were surveyed; 32 from Bandafassy, 28 from Oussadou, and 23 from Tenghory. All herds were single-household owned. The total number of animals within these flocks at the time of survey was 748, all of which were pure-bred West African Dwarf (WAD). The final data-set used for the analysis comprised 738 animals (with 10 animals excluded for missing data). In addition, there were a total of 18 entries and 142 exits recorded of pure-bred WAD. Ninety-five per cent of interviewees were male, with 98% of interviewees being a household head and 2% (2) ‘other household member’. All household heads were livestock owners, while the two ‘other [female] household members’ did not own the livestock. 8 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Interviewees’ perception of 12 month study period The distribution of scores for the interviewees’ perception of the 12 month study period in each site is given in Figure 3. Figure 3. Interviewees’ perception of 12 month study period for goat herds in the three sites Bandafassy Ousadou Tenghory Much worse than average Worse than average Average Better than average Site 0.0% 20.0% 60.0% 80.0% 100.0% Percent Overall, the great majority of interviewees perceived the year as average. Three per cent, 4% and 13% of interviewees in Bandafassy, Oussadou and Tenghory, respectively, rated the year as much worse than average, while in Bandafassy 6% rated the year as better than average. The remaining rated the year as average. 9Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal 3 Cattle results 3.1 Herd sizes and structure Herd size The surveyed cattle herd sizes ranged from 5 to 63 animals, with a mode (most frequent herd size) of 5 animals and a mean of 18 animals (Figure 4). All herds were single-household owned. Ninety-seven per cent of female cattle and 98% of male cattle were born in the herd. Figure 4. Distribution of cattle herd sizes 0 2 4 6 8 10 12 Number of herds 0 20 40 60 Herd size Age-by-sex structure The age-by-sex structure is shown in Figure 5. The combined herds comprised 15% calves ( ≤1 year of age), 38% subadults (>1 and ≤4 years of age), 37% adult females and 10% adult males. Overall there were 70% females. The majority of females (98%) were ≤15 years of age, and the majority of males (96%) were ≤7 years of age. The reasons for the drop in percentage of animals in age classes 1 and 2 are not clear, though possibilities are survey bias due to inaccurate recall, a low number of births one or two years before the 12 month period, high mortalities in year 0–1, exits of age class 1 animals by loan with return in later years. 10 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Figure 5. Age-by-sex structure in the surveyed cattle herds for females (F) and males (M) M F 5 Proportion of animals (%) 10 15 20 25 5 10 15 20 25 Age class (year) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 17 18 19 20 21 Age class 0 = animals ≤1 year of age, age class 1 = animals >1 year and ≤2 years of age etc. 3.2 Reproduction Parity in relation to age-class Figure 6 shows age class vs. parity (i.e. number of births per cow) for the full reproductive history data. The average age at first parturition cannot be accurately determined from these results (as, for example, an animal of parity 1 and current age 6, may have given birth when she was 6, 5 or 4 years old), but it appears the earliest age at first parturition is 4 to 5 years (and very infrequently 1 to 3 years). Other studies reported an average age of first parturition of 4.0–4.2 years (Agyemang et al. 1997; Otte and Chilonda 2002). Animals of second parity were mostly 6 to 9 years of age. For third parity, animals were mostly 7 to 9 years of age and for fourth parity animals were mostly 10 years of age. It can be noted that in a study of N’Dama cattle raised under extensive management conditions in southern Senegal, the average age of first calving was reported to be 5 years, with a range of 4 to 9 years (Ezanno et al. 2002). Figure 6. Parity in relation to age class for cattle (a sunflower plot where multiple points are shown as ‘petals’) 0 2 4 6 8 10 Age class (year) 0 2 4 6 8 Parity Age class 0 = animals ≤1 year of age, age class 1 = animals >1 year and ≤2 years of age etc. Cattle of age class >11 were discarded due to the potential unreliability of this data. 11Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Parturition rates Parturition rate by age class for the 12-month data is shown in Figure 7. It should be noted that from the age group >4 to >10 years the average parturition rate remains relatively constant. Figure 7. Annual parturition rates of female cattle, with 95% confidence intervals indicated Age class (year) Parturition rate (year) 0 1 2 3 4 5 6 7 8 9 10 11 0.5 1.0 1.5 2.0 Age class 0 = refers to animals of ≤1 year of age, age class 1 = refers to animals >1 year and ≤2 years of age etc. Cattle of age class >11 were combined into age class 11. Estimates of annual parturition rates, for both the 12-month data for females ≥ 3 and 4 years of age and the complete reproductive history of the females, are presented in Table 3. The estimates using the 12-month retrospective data may be the most accurate because they rely less on long-term recall than the complete reproductive history. Regardless, the calving interval recorded is very high at 2.3–2.6 years. In comparison, Agyemang et al. (1997) found an average parturition rate at 0.54, while Ba et al. (2011) found the parturition rate to be 0.72 for herds with 1–5 cows and 0.51 for herds with 6–19 cows. In the southern Senegal study by Ezanno et al. (2002) the average interval between parturitions was reported as 27 months, corresponding to an annual parturition rate of 0.44. Table 3. Various estimates of the annual parturition rates for female cattle Data Annual parturition rate (standard error) Interval between parturitions, in days3 (years) 12 month, all females ≥3 years of age 1 0.39 (0.01) 936 (2.6) 12 month, all females ≥4 years of age1 0.44 (0.02) 830 (2.3) Lifetime reproductive history of females2 0.40 (0.01) 913 (2.5) 1. Average annual rate of parturition based on number of parturitions of all females ≥3 or 4 years during the last 12 months. 2. Average annual rate of parturition based on total number of parturitions of all females born in herd, and ≤11 years of age. 3. 365/parturition rate. 12 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Other reproductive parameters Estimates of abortion rates for females ≥ 3 years of age and the lifetime reproductive history are given in Table 4. Of note is that the abortion rate was reasonably low using the 12-month data, whereas the abortion rate using the complete reproductive history was moderate. This difference may be due to differences in year effect (i.e. some years having greater abortion rates than others), or due to biases created from using a recall survey method. Table 4. Estimates of abortion for cattle Parameter Data source Value (standard errors) Annual abortion rate 12 month, all females ≥3 years of age 1, 2 0.01 (0.00) Lifetime reproductive history of females3 0.04 (0.00) 1. Average annual rate of abortion based on number of parturitions of all females ≥3 or 4 years during the last 12 months. 2. Similar results were obtained for all females ≤4 years of age. 3. Average annual rate of abortion based on total number of parturitions of all females born in herd, and ≤11 years of age. 3.3 Natural mortality The mortality rates are shown in Figure 8, and also given in Table 5 in section 3.4. The mortality rates were low for all age groups/sex, especially for males ≤ 1 year of age (0.00) and females >1 year of age (0.01). It was somewhat higher for females ≤1 year of age (0.04) and males >1 year of age (0.03). The overall mortality rate was 0.02, meaning that for a herd with a constant size of 18 animals over the year, 0.3 natural deaths would be expected annually. This is considerably lower compared to other results of cattle mortality in The Gambia (Agyemang et al. 1997), southern Mali (Ba et al. 2011) and sub-Saharan Africa (Otte and Chilonda 2002), which ranged from an overall mortality of 6–8% and a calf (≤ 1 year of age) mortality of 13–22%, particularly for calves. It should, however, be noted that these studies used a variety of methods and time frames to calculate the mortality, which differed from the 12MO survey methodology. This may have an effect on the results. Also, the instantaneous hazard rates given here differ from the overall probability of a natural death (see appendix 1), which is frequently used as an indication of mortality in literature. The difference between these rates are greater the higher the rate. Due to the low rates found for cattle mortality in this study there was no difference between the hazard rate and the probability1 (with 2 decimals). This said, the mortality rates presented here should be considered with care as they appear unrealistically low. Table 5. Annual offtake rates (standard errors) for cattle, for different offtake events Sex Age Offtake event Natural death Slaughter Sales, barters Loans, contracts Gift, dowry Withdrawal, theft Overall Female ≤1 year 0 0 0 0 0 0 0.04 (0.02) >1 year 0.01 (0.00) 0.04 (0.01) 0 0.01 (0.00) 0.01 (0.00) 0.06 (0.01) 0.01 (0.00) Male ≤1 year 0 0 0 0.03 (0.02) 0 0 0 >1 year 0 0.12 (0.02) 0 0.01 (0.01) 0.02 (0.01) 0.13 (0.02) 0.03 (0.01) Overall 0.01 (0.00) 0.06 (0.01) 0 0.01 (0.00) 0.01 (0.00) 0.08 (0.01) 0.02 (0.00) 1. Effect of offtake rates not included (Lesnoff et al. 2010). 13Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Figure 8. Annual mortality rates for natural death of cattle, for females (F) and males (M), with 95% confidence intervals indicated Mortality rate (/year) 0.1 0.2 0.3 0.4 0 1 F M 0 1 Age group Age group 0 = animals ≤1 year of age, and age group 1 = animals >1 year. 3.4 Offtake and intake Offtake rates Overall offtake rates, as well as offtake rates by individual events (i.e. slaughtering, sales/barter, loans/contracts, gifts/ dowry, withdrawal/theft) were given in Table 5. Rates of natural death (mortality) were included in this table for comparison purposes. The overall rate of annual offtake was 0.08, meaning that for a herd with a constant size of 18 animals over the year, 1.4 exits would be expected annually. This is slightly lower than the offtake observed by Ba et al. (2011) in mixed crop–livestock systems in southern Mali, who found an overall offtake rate of 0.11. This was mainly due to the offtake rate of females >1 year of age being higher than observed in this study. The single most important offtake event was sale/barter. The age class with the highest offtake via sales/barter was, by far, males >1 year of age. The main reasons for sale of animals were ‘ordinary’ (48%) and ‘emergency lack of feed’ (36%) followed by ‘emergency disease’ (12%) and ‘emergency traumatism’ (4%). For animals ≤1 year the only offtake recorded was for males for gift/ dowry. Intake rates The overall annual intake rate was 0.02, meaning that for a herd with a constant size of 18 animals over the year, 0.4 intake would be expected annually. Table 6 gives a breakdown by event (purchase/barters, loans/contracts, gifts/ dowry/inheritance). The only intake event was purchase/barter of animals >1 year of age. In comparison, Ba et al. (2011) found the overall intake rate to be slightly higher at 0.10, which was mainly due to a higher intake of females and males >1 year of age. 14 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Table 6. Annual intake rates for cattle, for different intake events Sex Age Intake event (standard errors) Purchases, barters Loans, contracts Gift, dowry, inheritance Overall Female ≤1 year 0 0 0 0 >1 year 0.02 (0.00) 0 0 0.02 (0.00) Male ≤1 year 0 0 0 0 >1 year 0.03 (0.01) 0 0 0.03 (0.01) Overall 0.02 (0.01) 0 0 0.02 (0.01) Net offtake Table 7 summarizes the annual net offtake. The overall net offtake rate was 0.06, meaning that for a herd with a constant size of 18 animals over the year, a net offtake of 1.1 animals is expected annually. The greatest net-offtake was for males >1 year of age. Table 7. Net offtake rates for cattle, as well as the underlying offtake and intake rates. Female (standard errors) Male (standard errors) Total ≤1 year of age >1 year of age ≤1 year of age >1 year of age Offtake 0 0.06 (0.02) 0 0.13 (0.03) 0.00 (0.01) Intake 0 0.02 (0.01) 0 0.03 (0.01) 0.02 (0.01) Net offtake 0 0.04 (0.02) 0 0.10 (0.03) 0.06 (0.01) 15Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal 4 Sheep results 4.1 Flock sizes and structure Flock size The surveyed sheep flock sizes ranged from 5 to 22 animals. The mode (most frequent flock size) was 5 animals (Figure 9), with a mean flock size of 9 animals. Almost all the animals ≤1 year of age (99%) and males >1 year of age (97%) were born in the flock, whereas only 79% of females >1 year of age were born in the flock. All sheep flocks were single household owned. Figure 9. Distribution of sheep flock size Number of flocks 0 5 10 15 20 25 0 5 10 15 Flock size Age-by-sex structure The age-by-sex structure is shown in Figure 10. The combined flocks comprised 25% females ≤1 year of age, 23% males ≤1 year of age, 44% females >1 year of age, and 8% males >1 year of age. Overall there were 69% females. The majority of females (96%) were ≤6 years of age, and the majority of males (95%) were ≤3 years of age. Note the drop in percentage of animals from age class 1 and 2 for males, which can mainly be explained by a high number of exits via sale in age classes 1 and 2. 16 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Figure 10. Age-by-sex structure in the surveyed sheep flocks for females (F) and males (M) Proportion of animals (%) M F 5 10 15 20 25 0 1 2 3 4 5 6 7 8 9 10 11 5 10 15 20 25 Age class (year) Age class 0 = animals ≤1 year of age, age class 1 = animals >1 year and ≤2 years of age etc. 4.2 Reproduction Parity in relation to age-class Figure 11 shows age class vs. parity for the full reproductive history data. The average age of first parturition cannot be determined from this data, but the earliest age at first parturition appears to be mainly at 2 years of age (with some at 1 year of age). Other studies of sheep in Senegal (Wilson 1991) and sub-Saharan Africa (Otte and Chilonda 2002) reported an average age of first parturition at 1.3–1.4 years. Animals of second parity are mostly 2 to 3 years of age, and that animals of third parity are mostly 4 years of age. Figure 11. Parity in relation to age class for sheep (a sunflower plot where multiple points are shown as ‘petals’) Age class (year) 0 2 4 6 8 0 2 4 6 8 10 Parity Age class 0 = animals ≤1 year of age, age class 1 = animals >1 year and ≤2 years of age etc. Sheep of age class >8 were discarded due to the potential unreliability of this data. 17Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Parturition rates Figure 12 shows parturition rate by age class for the 12 month data. The main increase in the annual parturition rate is seen from 0 to >2 years of age. Figure 12. Annual parturition rates of female sheep, with 95% confidence intervals indicated Age class (year) 0.5 1.0 1.5 2.0 Parturition rate (/year) 0 1 2 3 4 5 6 7 8 Age class 0 = animals ≤1 year of age, age class 1 = animals >1 year and ≤2 years of age etc. Sheep of age class >8 were combined into age class 8. Estimates of annual parturition rates, both for the 12 month data for females ≥1, 2, and 3 years of age and the complete reproductive history of the females, are presented in Table 8. The estimates using the 12 month data were sensitive to the minimum age chosen for reproductive females. The complete reproductive history gave the highest estimate. This difference may be due to differences in year effect (i.e. some years having greater abortion rates than others), or due to biases created from using a recall survey method. In comparison, the parturition rate was found to be 1.36–1.50 in Senegal (Wilson 1991). Table 8. Various estimates of the annual parturition rates for female sheep Data Annual parturition rate (standard error) Interval between parturitions, in days3 (years) 12 month, all females ≥1 year of age1 0.64 (0.04) 570 (1.6) 12 month, all females ≥2 years of age1 0.74 (0.05) 493 (1.4) 12 month, all females ≥3 years of age 1 0.79 (0.07) 462 (1.3) Lifetime reproductive history of females2 0.82 (0.03) 445 (1.2) 1. Average annual rate of parturition based on number of parturitions of all females ≥1, 2 or 3 years during the last 12 months. 2. Average annual rate of parturition based on total number of parturitions of all females born in herd, and ≤8 years of age. 3. 365/parturition rate. 18 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Other reproductive parameters Estimates of abortion rates for females ≥2 and ≥3 years of age, as well as the lifetime reproductive history, are given in Table 9. These were found to be somewhat high. Table 9. Estimates of abortion rates for sheep (standard errors) Parameter Data source Value Annual abortion rate 12 month, all females ≥2 years of age1, 2 0.04 (0.00) 12 month, all females ≥3 years of age 2 0.06 (0.01) Lifetime reproductive history of females3 0.08 (0.01) 1. Similar value was obtained for females ≥1 year of age. 2. Based on number of abortion of all females ≥2 or ≥3 years of age, respectively, during the last 12 months. 3. Based on total number of abortion of all females born in herd, and ≤7 years of age. 4.3 Natural mortality The mortality rates are shown in Figure 13, and also given in Table 10 in section 4.4. The mortality rate was moderately high for females ≤1 year of age (0.15) but low for females >1 year of age (0.03). For both age groups of males the mortality rate was moderate (0.07). Overall, the mortality rate was 0.06, meaning that for a flock with a constant size of 9 animals over the year, 0.5 deaths would be expected annually. In comparison, the annual mortality rates observed by Lesnoff (1999) in north Senegal was 0.10 for females and 0.15 for males, over all age classes. Recalculated to probabilities2 the mortality rate of natural death was 0.07–0.14 for lambs and 0.03 for females >1 year of age. For both lambs and ewes, this was considerably lower than the 26% lamb and 8% ewe mortality reported by Otte and Chilonda (2002) for sub-Saharan Africa. Figure 13. Annual mortality rates for natural death of sheep, for females (F) and males (M), with 95% confidence intervals Mortality rate (/year) Age group F M 0.1 0.2 0.3 0.4 0 1 0 1 Age group 0 = animals ≤1 year of age, and age group 1 = animals >1 year of age etc. 2. Effect of offtake rates not included (Lesnoff et al. 2010). 19Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Table 10. Annual offtake rates (standard errors) for sheep, for different offtake events Sex Age Offtake event Natural death Slaughter Sales, barters Loans, contracts Gift, dowry Withdrawal, theft Overall Female ≤1 year 0 0 0 0 0.01 (0.01) 0.01 (0.01) 0.15 (0.04) >1 year 0.01 (0.01) 0.09 (0.02) 0 0 0.03 (0.01) 0.14 (0.02) 0.03 (0.01) Male ≤1 year 0 0.01 (0.01) 0 0 0.03 (0.02) 0.04 (0.03) 0.07 (0.03) >1 year 0.13 (0.04) 0.46 (0.07) 0 0 0.06 (0.03) 0.65 (0.08) 0.07 (0.03) Overall 0.03 (0.07) 0.14 (0.02) 0 0 0.03 (0.01) 0.20 (0.02) 0.06 (0.01) 4.4 Offtake and intake Offtake rates The overall offtake rates, as well as the offtake rates by individual events (slaughtering, sales/barter, loans/contracts, gifts/dowry, withdrawal/theft) are given in Table 10. Rates of natural death (mortality) are included in this table for comparison purposes. The overall rate of annual offtake was 0.20, meaning that for a flock with a constant size of 9 animals over the year, 1.8 exits would be expected annually. It is of note that the overall rate of offtake was three times that of the overall mortality rate. The highest offtake rate, by far, was for sale/barter of animals, followed by withdrawal/theft, followed by slaughter. The main reasons for sale of animals were ‘ordinary’ (67%), followed by ‘emergency lack of feed’ (25%) and ‘emergency disease’ (7%). One per cent was sold due to ‘emergency traumatism’. Intake rates The overall rate of annual intake was 0.03, meaning that for a flock with a constant size of 9 animals over the year, 0.3 intakes would be expected annually. Table 11 gives a breakdown of input rate by event (i.e. purchase/barters, loans/ contracts, gifts/dowry/inheritance). The only intake observed was through purchase/barter. Table 11. Annual intake rates (standard errors) for sheep, for different intake events Sex Age Intake event Purchases, barters Loans, contracts Gift, dowry, inheritance Overall Female ≤1 year 0 0 0 0 >1 year 0.04 (0.01) 0 0 0.04 (0.01) Male ≤1 year 0 0 0 0 >1 year 0.02 (0.01) 0 0 0.02 (0.01) Overall 0.03 (0.01) 0.01 (0.00) 0.00 (0.00) 0.03 (0.01) 20 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Net offtake Table 12 summarizes the overall annual offtake and intake rates by sex and age classes. The highest rate of net offtake (at 0.65) was for males >1 year of age: from Table 10 it can be observed that this is primarily through sales/barter. The total net offtake rate was 0.17, meaning that for a flock with a constant size of 9 animals over the year, a net offtake of 1.5 animals is expected annually. Table 12. Net offtake rates for sheep, as well as the underlying offtake and intake rates (standard errors) Female Male Total ≤1 year of age >1 year of age ≤1 year of age >1 year of age Offtake 0.01 (0.01) 0.14 (0.02) 0.04 (0.02) 0.65 (0.09) 0.20 (0.01) Intake 0 0.04 (0.01) 0 0.02 (0.01) 0.03 (0.01) Net offtake 0.01 (0.01) 0.08 (0.02) 0.04 (0.02) 0.63 (0.09) 0.17 (0.01) 21Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal 5 Goat results 5.1 Herd sizes and structure Herd size The surveyed goat herd sizes ranged from 4 to 23 animals, with a mode (most frequent herd size) of 6 animals (Figure 14) and a mean herd size of 9 animals. All females ≤1 year of age were born in the herd, almost all males ≤1 year of age and females and males >1 year of age were born in the herd (90 and 96%, respectively). All goat herds were single household owned. Figure 14. Distribution of goat herd size Herd size 0 5 10 15 20 25 15 10 5 0 Number of herds Age-by-sex structure The age-by-sex structure is shown in Figure 15. The combined flocks comprised 30% females ≤1 year of age, 24% males ≤1 year of age, 40% females >1 year of age, and 6% males >1 year of age. Overall there were 60% females. The majority of females (96%) were ≤6 years of age, and the majority of males (98%) were ≤3 years of age. Note the drop in percentage for males in age classes 1 and above. This can mainly be explained by a high number of exits via sales and slaughters in age classes 1 and 2, combined with high mortality in age class. 22 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Figure 15. Age-by-sex structure in the surveyed goat herds for females (F) and males (M) M F 5 10 15 20 25 Proportion of animals (%) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 5 10 15 20 25 Age class (year) Age class 0 = animals ≤1 year of age, age class 1 = animals >1 year and ≤2 years of age etc. 5.2 Reproduction Parity in relation to age-class Figure 16 shows age class vs. parity for the full reproductive history data. The average age at first parturition cannot be determined from this study, but the earliest age at first parturition appears to be 1 to 2 years. Other studies gave an average age of first parturition of 1.0 year in Senegal (Wilson 1991) and 1.3 years in sub-Saharan Africa (Otte and Chilonda 2002). Animals of second parity are mostly 2 to 3 years of age (age classes 2 to 3), and animals of third parity mostly >3 to 4 years of age. Figure 16. Parity in relation to age class for goats (a sunflower plot where multiple points are shown as ‘petals’) Parity 0 2 4 6 8 0 2 4 6 8 Age class (year) Age class 0 = animals ≤1 year of age, age class 1 = animals >1 year and ≤2 years of age etc. Age class >8 were discarded due to the potential unreliability of this data. 23Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Parturition rates Figure 17 shows parturition rate by age class for the 12 month data. The drop in parturition rate for age classes 5 and 6 cannot readily be explained and require further investigation. Figure 17. Annual parturition rates of female goat, with 95% confidence intervals indicated 0 1 2 3 4 5 6 7 8 Age class (year) 0.5 0.1 1.5 2.0 Partiurition rate (/year) Age class 0 = animals ≤1 year of age, age class 1 = animals >1 year and ≤2 years of age etc. Goats of age class >8 were combined into age class 8. Estimates of annual parturition rates, for both the 12 month data for females ≥1, 2, and 3 years of age respectively and for the complete reproductive history of the females, are presented in Table 13. The estimates using the 12 month data were sensitive to the minimum age chosen for reproduction. The complete reproductive history gave a higher estimate of 0.90. This difference may be due to differences in year effect (i.e. some years having greater abortion rates than others), or due to biases created from using a recall survey method. In comparison the parturition rate was observed to be 1.4–1.6 for WAD goats in Senegal (Wilson 1991). Table 13. Various estimates of the annual parturition rates for female goat Data Annual parturition rate (standard error) Interval between parturitions, in days (years)3 12 month, all females ≥1 year of age1 0.64 (0.03) 570 (1.6) 12 month, all females ≥2 years of age1 0.75 (0.05) 487 (1.3) 12 month, all females ≥3 years of age 1 0.78 (0.06) 468 (1.3) Lifetime reproductive history of females2 0.90 (0.02) 406 (1.1) 1. Based on number of parturitions of all females ≥1, 2 or 3 years during the last 12 months. 2. Based on total number of parturitions of all females born in herd, and ≤8 years of age. 3. 365/parturition rate. 24 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Other reproductive parameters Estimates of abortion rate for females ≥2 years of age and the lifetime reproductive history are given in Table 14. Table 14. Estimates of abortion rates for goats (standard errors) Parameter Data source Value Annual abortion rate 12 month, all females ≥2 years of age1, 2 0.04 (0.00) Lifetime reproductive history of females3 0.08 (0.01) Annual net fecundity rate 12 month, all females ≥1 year of age 0.82 (0.11) 1. Similar values were obtained for all females ≥1 and ≥3 years of age. 2. Based on number of abortions of all females ≥2 years during the last 12 months. 3. Based on total number of abortions of all females born in herd, and ≤8 years of age. 5.3 Natural mortality Mortality rates are shown in Figure 18, and Table 15 in section 5.4. The mortality rate was moderately high for males >1 year of age (0.15), whilst it was low for males ≤ 1 year of age (0.04), females ≤ 1 year of age (0.03) and females >1 year of age (0.04). The overall mortality rate was 0.06, meaning that for a flock with a constant size of 9 animals over the year, 0.5 deaths would be expected annually. Recalculated to probabilities, 3 the mortality rate was 0.03–0.04 for kids, while doe mortality was 0.04 and male mortality was 0.14. This is considerably lower than the 24–28% kid mortality and 14–16% adult mortality found in other studies in Mali (Ba et al. 1996) and sub-Saharan Africa (Otte and Chilonda 2002). It follows the mortality rates presented here should be considered with care as they appear unrealistically low. Figure 18. Annual mortality rates for natural death of goats, for females (F) and males (M), with 95% confidence intervals indicated Age groups 0 0 1 0.4 0.3 0.2 0.1 F M 1Mortality rate (/year) Age group 0 = animals ≤1 year of age, and age group 1 = animals >1 year. 3. Effect of offtake rates not included (Lesnoff et al. 2010). 25Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal 5.4 Offtake and intake Offtake rates Overall offtake rates, as well as offtake rates by individual events (i.e. slaughtering, sales/barter, loans/contracts, gifts/dowry, withdrawal/theft) are given in Table 15. Rates of natural death (mortality) are included in this table for comparison purposes. The overall rate of annual offtake was 0.14, meaning that for a flock with a constant size of 9 animals over the year, 1.3 exits would be expected annually. It is of note that the overall rate of offtake is approximately twice the overall mortality rate. The highest offtake rate was due to sale/barter, followed by slaughter, followed by withdrawal/theft. The main reasons for slaughter of animals was ‘emergency lack of feed’ (43%) followed by ‘ordinary’ (38%) and emergency disease (16%). Three per cent were sold due to ‘emergency traumatism’. Table 15. Annual offtake rates (standard errors) for goats, for different offtake events Sex Age Offtake event Natural death Slaughter Sales, barters Loans, contracts Gift, dowry Withdrawal, theft Overall Female ≤1 year 0 0 0 0 0.08 (0.01) 0.08 (0.01) 0.03 (0.02) >1 year 0.02 (0.01) 0.10 (0.02) 0 0 0.01 (0.01) 0.13 (0.02) 0.04 (0.01) Male ≤1 year 0 0 0 0 0.01 (0.01) 0.01 (0.01) 0.04 (0.02) >1 year 0.13 (0.04) 0.27 (0.05) 0 0 0.07 (0.03) 0.46 (0.07) 0.15 (0.04) Overall 0.03 (0.01) 0.09 (0.01) 0) 0 0.02 (0.01) 0.14 (0.01) 0.06 (0.01) Intake rates The overall rate of annual intake was 0.03, meaning that for a flock with a constant size of 9 animals over the year, 0.3 intakes would be expected annually. Table 16 gives a breakdown of input rate by event (i.e. purchase/barters, loans/contracts, gifts/dowry/inheritance). The only intake event was purchase/barter of animals. Table 16. Annual intake rates (standard errors) for goats, for different intake events Sex Age Intake event Purchases, barters Loans, contracts Gift, dowry, inheritance Overall Female ≤1 year 0 0 0 0 >1 year 0.03 (0.01) 0 0 0.03 (0.01) Male ≤1 year 0 0 0 0 >1 year 0.05 (0.02) 0 0 0.05 (0.02) Overall 0.03 (0.01) 0 0 0.03 (0.01) 26 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Net offtake Table 17 summarizes the annual offtake and intake rates, combined for all events, by sex and age classes. The highest rate of net offtake (at 0.41) was for males >1 year of age: from Table 15 it can be observed that this is primarily through sales/barter. The overall net offtake rate was 0.11, meaning that for a flock with a constant size of 9 animals over the year, a net offtake of 1.0 animal is expected annually. Table 17. Net offtake rates for goats, as well as the underlying offtake and intake rates (standard errors) Female Male Total ≤1 year of age >1 year of age ≤1 year of age >1 year of age Offtake 0.08 (0.01) 0.13 (0.02) 0.01 (0.01) 0.46 (0.07) 0.14 (0.02) Intake 0 0.03 (0.01) 0 0.05 (0.02) 0.03 (0.01) Net offtake 0.08 (0.01) 0.10 (0.02) 0.01 (0.01) 0.41 (0.07) 0.11 (0.02) 27Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal 6 Discussion The purposes of this survey were: i) to estimate demographic parameters for herds/flocks in the PROGEBE-Senegal project sites, which combined with other information sources, could be used for prioritizing project interventions; ii) to compare demographic productive parameters between ERL and non-ERL; and iii) to be used as a baseline for evaluating impacts of project interventions. The survey was not designed to evaluate demographic productivity parameters over the long-term, which should be kept in mind when reading the discussion. For validation of the results and evaluation of demographic productivity parameters over the long-term, a long-term longitudinal survey is recommended. The major results found and their implication for prioritizing future project interventions are discussed, as well as the suitability of using the data as a baseline for evaluating impact of project interventions. Due to the very low number of non-ERL found within the surveyed sites (0–0.1% of surveyed animals), a comparative analysis of ERL and non-ERL demographic parameters was not possible. However, the implications of this finding on project priorities and future breeding strategies are discussed in brief. 6.1 Key demographic parameters An important result is that the reproductive parameters for all species reported here appeared somewhat worse than found in other studies (Wilson 1991; Otte and Chilonda 2002; Ba et al. 2011). The age at first calving for cattle (generally 4 to 5 years), and especially the age at first lambing/kidding for small ruminants (generally 2 years) is higher than the 4.0–4.2 years found for cows and 1.0–1.4 found for small ruminants. Although not investigated here, it is reasonable to assume that this is primarily due to differences in management practices. Improved management to decrease the average age at first parturition (e.g. feed supplementation) should be considered as a potential PROGEBE intervention. The abortion rate was found to be moderately high for sheep (0.06) and moderate for goats (0.04). Abortion in sheep and goats in the humid tropics of West Africa have been found to mainly be associated with starvation and diseases (Oppong 1988). Improved management of feed resources and diseases for sheep and goats in order to decrease the abortion and stillbirth rate should therefore also be considered. Another key finding was the moderately high mortality rates of female sheep ≤1 year of age and male goats >1 year of age (0.15), as well as the moderate mortality rates of male sheep of both age classes (0.07). It is thus suggested that addressing mortality of the small ruminants, and especially sheep, should be one of PROGEBE’s priority interventions, and this is likely best addressed through change in management practices such as improved feed and disease control (including the increased use of dewormers particularly for small ruminants). For other species and age class combinations, mortality rates were on the lower side of those reported elsewhere and thus should be considered with care as they may not depict the true situation. 28 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal In the much longer term (20 to 50 years) it may be possible to increase reproductive performance and reduce mortality of the animals through a breeding program (as well as positively influence other traits of interest such as growth rate and milk production). Caution needs to be taken, however, for interventions targeting a shorter parturition interval, as due to lactation anoestrous a shorter milking period resulting in the need to supplement young animals may result. Note that a long-term approach to any within-breed improvement program is essential, as within a typical breeding nucleus only about a 1 to 3% change in mean performance can be affected per annum (Falconer and Mackay-Longman 1996) and, should a tiered breeding structure be utilized, the average genetic merit of animals in the lower tiers will lag behind the average genetic merit of animals in the nucleus. 6.2 Findings on existing breeding strategies and their implications All three ERL had animals not born within the herd/flock. However, the proportion of introduced animals was very low (1–4%) for all species/age/sex groups except female sheep and goat >1 year of age (21 and 10%, respectively). The use of ‘outside’ animals as breeding animals is important to keep the rate of inbreeding to an acceptable level and should therefore be encouraged (inbreeding is caused by the mating of relatives and typically results in reduced fitness and reproductive ability). Furthermore, it was found that males only make up 6–10% of the herds/flocks (depending on species), which suggests that controlled breeding is used across species. It is, however, uncertain whether the males remaining in the flock are genetically superior, or whether the genetically superior males are sold (as e.g. they can fetch higher market prices due to corresponding phenotypic superiority) leaving the inferior males as breeding animals. In addition, it was found that the main exit event was sale/barter (0.04, 0.14 and 0.09 for cattle, sheep and goats, respectively), while slaughter of animals was limited (0.01, 0.03 and 0.03 for cattle, sheep and goats, respectively). This indicates that sale/barter of animals is more important for keeping goats and especially sheep, compared to cattle. Furthermore, it indicates that domestic consumption is not a priority for any of the species. This should be taken into consideration when prioritizing PROGEBE interventions. The PROGEBE-Senegal household survey (ILRI 2011) further indicated that knowledge and use of breeding strategies is low. Capacity building programs on basic principles and practices of breeding, as well as management practices to reduce mortality and improve other key parameters, are thus recommended to improve awareness of traditional and alternate breeding and management practices on livestock performance. The finding that virtually all ruminant livestock within the surveyed sites were ERL (99.9% for cattle and 100% for sheep and goats) is supported by the results of the PROGEBE-Senegal household survey (100% for all species) (see ILRI 2011). These results clearly indicate that the populations of ERL in the project intervention sites are currently not marginalized due to the introduction of non-ERL. The above results also show that non-ERL are mainly found in sheep flocks and to a lesser extent cattle herds, while the presence of non-ERL is insignificant in goats flocks. This difference between species could be due to a range of factors such as: gender differentiated ownership; availability and suitability of non-ERL breeds; external support etc. 29Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal 6.3 Considerations for use of survey data The demographic parameters presented here can be used as baseline parameters for PROGEBE but with care as they relate to a particular 12 month interval, which is subject to a particular set of environmental conditions. If a follow-up survey is performed in a year rated different to the baseline year it may be difficult to estimate the impact of project interventions. For example, if project interventions have had a positive impact on the demographic parameters reported here, but a follow-up survey is performed in an unusually poor year, the parameters will (artifactually) appear to have either stayed the same or become worse. Conversely, if project interventions have had no impact on the demographic parameters reported here, but a follow-up survey is performed in an unusually good year, the parameters will (artifactually) appear to have improved. The demographic parameters estimated here, combined with other data (such as that from the household survey and livestock census), can also be used to model the expected impact of breeding interventions. For example, for a particular breeding strategy (e.g. with a given nucleus size, number of multiplier units etc.) it is possible to estimate the per cent genetic improvement of the commercial animals in say 10, 20, 30 etc. years. Ideally the per cent genetic improvement would then be translated to a more meaningful indicator such as value to households (e.g. increased income) or value to the livestock industry. Alternatively the model could be used to back-calculate the size of the breeding program required to give a pre-set level of genetic improvement (or improvement in an alternate indicator) in the commercial population within a certain time frame. It is strongly recommended that such an exercise be conducted in the near future to assist in the planning of PROGEBE breeding activities. 30 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal 7 Conclusions and summary of main recommendations The findings of this survey clearly indicate that N’Dama cattle, Djallonke sheep, and WAD goats are the prominent breeds in the PROGEBE-Senegal project areas and suggests that some level of controlled breeding seems to be applied in most herds/flocks, primarily through sire selection (although these may or may not be implemented with a specific breeding objective in mind). There seem to be a considerable scope for improvement of especially reproductive demographic parameters through improved herd/flock management in the short term, and possibly breeding strategies in the long term. Specifically, it can be recommended that PROGEBE consider/prioritize the following issues for future project activities or interventions: Interventions towards lowering the natural mortality. In the short to medium term (next few to 20 years) this • should mainly be through changes to management practices. The results from the PROGEBE Senegal household survey (ILRI 2011) suggest that the main areas of intervention should be in relation to diseases and feed resources. However, any scheme of interventions should be based on local conditions and further investigations are required in this regard. In the much longer term (20 to 50 years) it may be possible to reduce mortality by genetically improving the animals through a breeding program. Interventions to improve reproductive parameters should be prioritized, namely, age at first parturition, • parturition interval and abortion rates. Again, this should mainly be through changes in management practices in the short-term, such as improved feeding, while in the longer term these parameters could potentially be improved through genetic improvement. Capacity building programs to improve awareness of traditional and alternate management and breeding practices • and the effect these have on livestock production and productivity. A modelling study using the demographic parameters estimated here, combined with other data from the • household survey, livestock census and literature to determine the expected impact of potential PROGEBE interventions (such as improved health-care, feeding and/or animal genetic improvement) over different time horizons. 31Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal References Agyemang, K. 2005. Trypanotolerant livestock in the context of trypanosomiasis intervention strategies. PAAT Technical and Scientific Series 7, Rome: Food and Agriculture Organization of the United Nations. Agyemang, K., Dwinger, R.H., Little, D.A. and Rowlands, G.J. 1997. Village N’Dama cattle production in West Africa— Six years of research in The Gambia. Nairobi: International Livestock Research Institute. Ba, S.E., Udo, H.M.J. and Zwart, D. 1996. 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Agricultural Systems 61:207–221. Lesnoff, M. 2008. Evaluation of 12-month interval methods for estimating animal-times at risk in a traditional African livestock farming system. Revue D’élevage et de Médecine Vétérinaire Des Pays Tropicaux 85:9–16. Lesnoff, M., Messad, S. and Juanés, X. 2009. A cross-sectional retrospective method for estimating livestock demographic parameters in tropical smallholder farming systems. Paris: French Agricultural Research Centre for International Development. Lesnoff, M., Messad, S. and Juanes, X. 2010a. 12MO: A cross-sectional retrospective method for estimating livestock demographic parameters in tropical smallholder farming systems. Paris: French Agricultural Research Centre for International Development. Lesnoff, M., Lancelot, R., Moulin, C.-H., Messad, S., Juanès, X. and Sahut, C. 2010b. Calculation of demographic parameters in tropical livestock herds—A discrete time approach with LASER animal-based monitoring data. http://livtools.cirad.fr Murray, M. and Trail, J.C.M. 1984. Genetic resistance to animal trypanosomiasis in Africa. Preventive Veterinary Medicine 2:541–551. Oppong, E. 1988. Health control for sheep and goat in the humid tropics of West Africa. In: Timon, V.M. and Baber, R.P. (eds), Sheep and goat meat production in the humid tropics of West Africa. FAO Animal Health Paper 70. Rome: Food and Agriculture Organization of the United Nations. Osaer, S., Goossens, B., Kora, S., Gaye, M. and Darboe, L. 1999. Health and productivity of traditionally managed Djallonke sheep and West African Dwarf goat under high and moderate trypanosomosis risk. Veterinary Parasitology 82:101–119. Otte, M.J. and Chilonda, P. 2002. Cattle and small ruminant production systems in sub-Saharan Africa—A systematic review. Rome: Food and Agriculture Organization of the United Nations. 32 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Rischkowsky B. and Pilling, D. (eds). 2007. The state of the world’s animal genetic resources for food and agriculture. Rome: Food and Agriculture Organization of the United Nations. Snow, W.F., Wacher, T.J. and Rawlings, P. 1996. Observations on the prevalence of trypanosomiasis in small ruminants, equines and cattle, in relation to tsetse challenge, in The Gambia. Veterinary Parasitology 66:1–11. UNDP (United Nations Development Programme). 2007. Sustainable management of globally significant endemic ruminant livestock of West Africa—Project Document. Governments of The Gambia, Guinea, Mali and Senegal, GEP/UNDP, UNOPS. PIMS 1119. Wilson, R.T. 1991. Small ruminant production and the small ruminant genetic resource in tropical Africa. FAO Animal Production and Health Paper. Rome: Food and Agriculture Organization of the United Nations. Zaibet, L., Traore, S., Ayantunde, A., Marshall, K., Johnson, N. and Siegmund-Schultze, M. 2011. Livelihood strategies in endemic livestock production systems in subhumid zone of West Africa: Trends, trade-offs and implications. Environment, Development and Sustainability 13(1):87-105. 33Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal Appendix 1: Illustrative example of instantaneous hazard rates in relation to this survey Assume a 12 month retrospective survey, from which we will calculate annual instantaneous hazard rates (referred to as rates below for short). The herd/flock structure, and events happening during the 12 month survey period, are as follows: Sex, age Number of animals at the start of the 12 month period Events (each uniformly distributed across the year) Number of animals at the end of the 12 month period, i.e. at time of survey Females ≤1 year 3 2 deaths. Birth of 2 females and 1 male offspring (from females >1 year) 2 (the 2 females born) Females >1 year 6 1 adult female purchased 8 (the 6 initial + the 1 remaining young female which is now >1 year of age + the 1 purchased) Males ≤1 year 1 (the 1 male born) Males >1 year 1 1 Total 10 12 The hazard rate (h) for a particular category (sex and age class) is calculated as the number of events ( m) divided by the time the animals have spent in that category (T): h = m/T. If all of the above data were available we would calculate T as the average of the number of animals in a particular category at the start and end of the 12 month period. Examples: The overall mortality rate is = 2/11 = 0.18, as there were 2 mortalities across all age-sex classes and T = (10+12)/2 • = 11. Thus for a herd with a constant size of 100 animals over the year, 18 deaths would be expected annually (as 0.18 * 100 = 18). The mortality rate for young females is 2/2.5 = 0.80, as there were 2 mortalities of young females, and T = (3+2)/2 • = 2.5. Thus for a herd with a constant size of 20 young females over the year, 16 deaths of young females would be expected annually (as 0.80 * 20 = 16). The overall purchase rate is 1/11 = 0.09, as there was 1 purchase across all age-sex classes and T = (10+12)/2 = • 11. Thus for a herd with a constant size of 50 animals over the year, 4.50 purchases would be expected annually (as 0.09 * 50 = 4.50). The parturition rate for females >1 year of age is 3/7 = 0.43, as there were 3 births to adult females and T = T • = (6+8)/2 = 7. Thus for a herd with a constant size of 10 adult females over the year, 4.3 parturitions would be expected annually (as 0.43 * 10 = 4.3). 34 Sustainable management of globally significant ERL in West Africa: Estimate of livestock demographic parameters in Senegal In reality, however, the number of animals at the start of the 12 month period is not known (as the survey is retrospective and being conducted at the end of the 12 month period). This is thus approximated as ‘the number of animals present at the time of the survey – entries over the 12 months + exits over the 12 months’. For the above example, over all sex-age classes, it is: [12 animals present at time of survey] – [3 births + 1 purchase] + [2 deaths] = 10. This concept is extended to individual age classes. The number of animals within a particular age class ( i) at the start of the survey is approximated as ‘the number of animals present at the time of survey in age class i + 1 – 0.5 * (net entries for age class i ) – 0.5 * (net entries for age class i + 1 )’. The 0.5 is because we assume that animals enter/exit age classes uniformly throughout the year, thus on average each animal spends half a year in the herd. Relationship between hazard rates and probabilities It is important to note that hazard rates are not the same as probabilities. The equation relating hazard rates to probabilities is as follows: where p is the probability, h the hazard rate, and t the length of the decomposition unit. For example, in this survey an annual instantaneous mortality rate of 0.5, would correspond to an annual probability of death of 0.39, as: Thus 39% of animals (rather than 50%) would be expected to die within a year. For more details in relation to this, including theoretical background, see Lesnoff et al. (2010b). Sustainable management of globally significant endemic ruminant livestock in West Africa: Estimate of livestock demographic parameters in Senegal RESEARCH PROGRAM ON Livestock and Fish ILRI R esearch Repo rt 2 9 IL R I R E S E A R C H R E P O R T 29 ISBN 92–9146–277–2 CGIAR is a global agricultural research partnership for a food-secure future. Its science is carried out by15 research centres that are members of the CGIAR Consortium in collaboration with hundreds of partner organizations. cgiar.org The International Livestock Research Institute (ILRI) works to enhance the roles livestock play in pathways out of poverty in developing countries. ILRI is a member of the CGIAR Consortium, a global research partnership of 15 centres working with many partners for a food-secure future. ILRI has two main campuses in East Africa and other hubs in East, West and southern Africa and South, Southeast and East Asia. ilri.org