BIOLOGICAL RHYTHM RESEARCH
https://doi.org/10.1080/09291016.2018.1558740
REVIEW ARTICLE
Factors influencing seasonal anestrus in buffaloes and
strategies to overcome the summer anestrus in buffaloes
Kennady Vijayalakshmya, Ranjeet Vermab, Habibur Rahmanc,
Hanuman Prasad Yadavd, Meenakshi Virmania, Dharmendra Kumare
and Vikas Choudhiryf
aAnimal Physiology Division, Lala Lajpat Rai University of Veterinary & Animal Sciences, Hisar, India;
bAnimal Reproduction Division, Indian Veterinary Research Institute, Izatnagar, India; cRegional
Representative for South Asia, International Livestock Research Institute, New Delhi, India; dDivision of
Veterinary Gynaecology and obstetrics, ICAR- National Dairy Research Institute, Karnal, India; eAnimal
Physiology and Reproduction Division, ICAR – Central Institute for Research on Buffaloes, Hisar, India;
fDepartment of Veterinary Gynaecology and Obstetrics, NDUAT, Faizabad, India
ABSTRACT ARTICLE HISTORY
Reproductive managements of buffalo during the summer season Received 23 November 2018
a challenging task livestock’s owner. There are different factors con- Accepted 2 December 2018
tributes to this condition; the most important are consequence of KEYWORDS
increased temperature and humidity that result in a decreased Buffalo; anestrus; climate;
expression of overt sings of estrus and reduction in appetite and reproductive managements
dry matter intake. The failure to express the overt signs of estrus is
due to aberration in endocrine profile. Heat stress during the summer
causes hyper-prolactinaemia, suppressing the secretion of gonado-
tropins, which alters the ovarian steroidogenesis. It also affects folli-
culogenesis, follicular fluid microenvironment and oocyte quality.
A large number of hormonal regimens have been used with varying
degree of efficacy in terms of estrus induction and conception rate.
A combined strategy of improvement in environment, nutrition and
management is pre-requisite for hormonal manipulation in order to
improve productivity of buffaloes during the summer season.
Introduction
Buffaloes are designated as the “Black Gold” in Indian sub-continent due to their high
productive potential. The species is distributed over more than 40 countries of the world
(Gordon 1996) and the population increased from 159 million (FAOSTAT 1997) to
177 million (FAOSTAT 2007). Buffaloes are raised in India mainly because of milk with
higher fat percentage and meat. The species has been traditionally regarded as poor
breeder having low fertility in the majority of conditions under which they are raised
(Barile 2005). They suffer from some inherent reproductive problems characterized by
delayed puberty and sexual maturity, seasonality in reproduction, silent estrus, poor
estrus signs and prolonged postpartum service period, etc.. Domestic buffalo exhibits
suspension of sexual activity during summer in almost all parts of the world (Shah 1990),
manifests late maturity, long postpartum anestrous intervals, poor expression of estrus,
CONTACT Kennady Vijayalakshmy drviji.vet6115@yahoo.com
© 2018 Informa UK Limited, trading as Taylor & Francis Group
2 K. VIJAYALAKSHMY ET AL
poor conception rates (CRs) and long calving intervals. This condition is popularly known
as summer anestrus and incidence generally varies between 36.6% and 59.5%. Buffaloes
with summer anestrus fail to exhibit estrus as a result of aberration in the endocrine
profile leading to ovarian inactivity. Increased day length with high environmental
temperature causes hyper-prolactinaemia, suppressing secretion of gonadotropins
which leads to an alteration in ovarian steroidogenesis. Heat stress also affects follicu-
logenesis, follicular fluid microenvironment and oocyte quality. Summer anestrus is
a multifactorial condition, caused by environmental, nutritional, hormonal and manage-
mental factors. Alleviating these etiological factors, the reproductive efficiency can be
improved in this species. In the present manuscript, a brief description of the factors
causing summer anestrus and available management and therapeutic practices are
discussed.
Seasonality in the reproductive pattern
Buffaloes are polyestrus species and show estrus year around. However, a distinct
seasonal pattern has been reported from different countries of the world including
India, Pakistan and many other parts of the world (Gangwar 1980; Barile 2005). This
has been attributed to environmental factors especially ambient temperature, photo-
period and feed supply, more than the genetic factors (Zicarelli 1994). More accu-
rately, the species is seasonally polyestrus with distinct seasonal variation in the
display of estrus, conception and calving. The expression of estrus is limited during
colder months of winter, while sex vigour declines during the hot summer (Misra and
Sengupta 1965). The indirect effect of climate on the vegetation pattern seems to be
most influential in buffalo’s natural reproductive pattern during the summer season.
The photoperiod has a marked influence on the reproductive pattern through the
pineal gland secretion that controls the shift. In contrast, buffaloes breed throughout
the year in some areas of the world, but more in the spring and a little less in
autumn.
Factors causing summer anestrus
Summer anestrus in buffaloes is a multi-factorial condition. The main contributing factors
are kind of environmental, nutritional, endocrine and managemental.
Environmental factors
Ambient temperature, humidity and photoperiod play important role causing anes-
trus in buffaloes during the summer. It was reported that ambient temperature and
relative humidity exert a direct effect on breeding efficiency (Roy et al. 1968).
Unlike favourable environment, the high temperature and humidity causes aberra-
tion in the cycle length and shorter duration of estrus. Heat stress has a direct
effect on neuro-endocrine setup in buffalo (Razdan 1988) because of their suscept-
ibility to thermal stress (Pandey and Roy 1966) during the summer, especially when
exposed to the direct sun rays as they have poor cutaneous evaporative cooling
mechanism owing to low density of sweat glands. Buffaloes get little protection by
BIOLOGICAL RHYTHM RESEARCH 3
virtue of their black skin and scanty hair coat (Cockrill 1993). High relative humidity
further accentuates the condition (Misra et al. 1963). The duration and intensity of
light exposure to animals also influence the onset of the oestrous cycle (Zicarelli
1997).
Nutritional factors
Elevated temperature depresses feed consumption during the summer in tropical and
sub-tropical conditions (Marai et al. 2002). The quantity of consumed nutrients, dry
matter (DM) intake including crude protein declines and a negative nitrogen balance
may occur (West 1999) during the summer due to heat stress. DM digestibility and
protein/energy ratio is also reported to be decreased in heat stressed animals (Moss
1993). Further, the digestibility coefficient for each of DM and crude protein is also found
significantly lower in the summer than winter in lactating Murrah buffaloes (Verma et al.
2000). Digestion and metabolism of non-pregnant buffaloes declined with exposure to
2–3 h solar radiation at an air temperature of 42°C (Zhengkang et al. 1994) and nitrogen
retention decreased significantly under heat stress.
Buffaloes are generally reared under low input–output management system
(Jainudeen 1989). In cattle, the nutritional stress alters the feedback mechanism
between oestradiol and LH surge which reduces the sensitivity of follicles to gonado-
tropins (De Rensis and Scaramuzzi 2003), the mechanism perhaps similar in buffalo, but
allied information is lacking in the said species. Several macro and micronutrients are
found to be in a lower order in various types of anestrus buffaloes Abou-Zeina et al.
(2009). The serum levels of Zn, Cu and Co are also documented to be lower than the
normal level in anestrus buffaloes (Singh et al. 2006). Iron and copper are used routinely
as an indicator for FSH, LH and oestrogen activity (Desai et al. 1982) and are found in
decreased level in anestrus buffaloes than cycling animals (Yessein et al. 1994).
Phosphorous deficiency Abou-Zeina et al. (2009), and hypocuprosis due to low cop-
per–molybdenum ratio was reported to cause anestrus during the summer (Randhawa
et al. 2004). Although, a large number of studies have been documented in relation to
mineral profile in anestrus buffaloes but are inconclusive.
Endocrine factors
Heat stress is a major contributing factor to the low fertility of buffalo in the late summer
months. Effects of heat stress on reproductive hormones and other physiological functions are
a direct consequence of the increase in body temperature (De Rensis and Scaramuzzi 2003;
Khodaei Motlagh 2003). Prolactin is directly associated with the ambient temperature
(Wettemann and Tucker 1974) and may mediate the seasonal effects on reproduction in
buffalo (Singh and Chaudhry 1992). During hot summer months, buffaloes show hyper-
prolactinaemia (Singh and Chaudhry 1992), which is attributed to the seasonal changes in
pineal metabolism (Paraneswaran et al. 1983) and proposed to be a possible cause of summer
anestrus in the species (Singh and Madan 1989). Prolactin may block the hypothalamic
mechanism responsible for episodic release of LH or inhibit the positive feedback of estrogen
on LH secretion, thus interferes with estrus cycle and fertility. At the ovarian level, it alters the
number of LH receptors for ovarian steroidogenesis and ovaries become refractory to the
4 K. VIJAYALAKSHMY ET AL
influence of FSH and LH (Sheth et al. 1978). Further, the optimal LH surge is also reported to be
absent in anestrus buffaloes in the summer. It was reported that the ratio of FSH to LH is lower
in hot summer months compared with peak breeding season (Janakiraman et al. 1980).
Anestrus associated with low thyroid function is common in buffaloes during the summer
season (Gupta and Dhoble 1988) and had been postulated that high ambient temperature
leads to hypothyroidism, which results in the reduced responsiveness of ovary to pituitary
gonadotropins causing summer infertility (Roy et al. 1968).
The low reproductive efficiency of buffaloes in the summer has also been attributed to
low luteal activity (Madan 1984) which is characterized by lower mean progesterone level as
well as the lower peak of progesterone level during the summer (Harjit and Arora 1982;
Qureshi et al. 2000), perhaps the reason for poor conception. Estradiol concentration is
reported to be low in anestrus rural buffaloes during the summer (Jain 1988; Sarvaiya et al.
1993). A high level of serum corticoids was reported in anestrus buffaloes exposed to
thermal stress during the summer and a higher level of serum corticoids leads to an altered
gonadotropin secretion, which ultimately triggers the state of anestrus Singhal et al. (1984).
Management factors
Management plays an important role in rearing of buffalo during the summer season. It
is well-known that buffaloes are weak in estrus exhibition (Jainudeen 1988) which is
further exacerbated during the hot season (De Rensis and Lopez-Gatius 2007). Majority
of the buffalo during the summer shows silent estrus (Chaudhry 1988), characterized by
less intense signs of estrus with shorter duration (Jainudeen and Hafez 2000). It was
found that buffaloes tend to exhibit estrus mostly during the night or morning hours,
which remain unnoticed by most of the farmers. So routine observation does not help
much in the detection of estrus in buffaloes (Beg and Totey 1999) leading to prolonged
service period during warmer months, Bughio et al. (2000).
Strategies for summer anestrus
Various strategies like environmental modification, improved nutrition, breeding, suck-
ling management and hormonal therapy can be employed to improve the reproductive
efficiency in buffaloes (Gupta and Das 1999).
Management practices
Summer breeding of buffaloes can be successfully carried out by changing farm man-
agement practices, Roy et al. (1968) to improve the efficiency of rural buffaloes reared
under field conditions (Pant et al. 2002). Protection from direct solar radiation is the
principle of real management in the species during hot summer months which includes
provision of shade, loose housing system and application of water to the body surface
by sprinkling or washing or providing wallowing (Razdan 1988). It has been shown that
showers in addition to wallowing facilities increase the CR reported by Di Palo et al.
(2009). Proper and extensive housing system and a shift from day to night grazing
practices help in reducing the adverse effects on fertility and productive efficiency in
buffalo during the summer (Razdan 1988; Neglia et al. 2009).
BIOLOGICAL RHYTHM RESEARCH 5
Improving estrus detection methods
Poor estrus detection is one of the factors that increase the calving conception interval
of buffalo. The routine heat detection measures used traditionally in buffalo are inade-
quate to detect estrus during the summer season (Jainudeen and Hafez 2000) and thus
use of an entire male during the cooler part of the day or night hours may improve the
efficiency of estrus detection (Acharya 1988). In the field condition, observing the animal
in the night and early morning for the signs of estrus would be beneficial to detect
buffaloes in estrus. It is also to be kept in mind that estrus behaviour in buffalo has
a lower intensity than in cows, hence requires critical watch to the animal and differently
than the cows. Bellowing and homosexual mount is less pronounced in buffalo. Further,
buffalo heifers show in frequent bellowing, differently than the buffalo cows showing
continuous. Quantity of cervical discharge is less and may vary between 5 and 25 ml in
buffalo heifers, requires closer look in the morning hour’s detection.
Hormonal treatments
Various hormonal treatment regimens are followed to alleviate anestrus and stimulate
ovarian activity, to induce or synchronize behavioural estrus or control ovulation (Barile
2005; De Rensis and Lopez-Gatius 2007). Different hormones were used either alone or in
combinations producing varied degrees of success. Progesterone-based treatment regi-
mens (PRID, CIDR, CRESTAR, Progesterone injections) either alone observed by Singh et al.
(1983) or in combination with gonadotropins and PGF2α reported by Neglia et al. (2003)
proved to be very effective in inducing ovarian activity in the summer anestrus buffaloes.
Nutritional management
Feeding strategy for buffaloes during hot climate is imperative in reducing infertility
problems especially summer anestrus. Provision for night feeding, grazing only in the
morning and late in the afternoon can reduce the heat stress in buffaloes. Moreover,
feeding green fodder or silage or hay, ad-libitum water and mineral mixture supple-
mentation improve the efficiency of reproduction during the summer. Buffaloes if well
fed can be detected in estrus during the night in the summer for regular breeding (Harjit
and Arora 1982). Grazing animals have to be supplemented with minerals particularly
with those which are deficient in forages or fodders and the energy balance also has to
be maintained in the ration. Feeding buffaloes on roughage during the night will reduce
the heat load on the animal (Acharya 1988).
There are several key areas of nutritional management which should be considered
during hot weather. These include formulation for reduced DM intake, greater nutrient
requirements during hot weather, dietary heat increment and avoiding nutrient excess.
Indigenous Technical Knowledge (ITK)/herbal treatments
Themajority of the farmers use ITK to overcome the anestrus problems in buffaloes during the
summer by offering locally available resources in different combinations. Perhaps in many
cases, there are inadequate veterinary facilities at the village level; hence there is no alternative
6 K. VIJAYALAKSHMY ET AL
to accept the adoption of ITK/herbals for the treatment of their buffaloes, due to low costs of
ITKs and availability. It was observed that the majority of animals (53.33%) overcome anestrus
by keepingmale with the female in practice; 45.00% by using boiledMaithi (Trigonella foenum
graecumL.) with Wheat bran for three days; 38.84% by feeding 0.5–1 kg boiled Bajara
(Pennisetum typhoidesL.) mixed with Gur (Jaggery) for a week, and 30.24% by feeding
0.5–1 kg Masurdaal (Lens esculentamoench) in evening time. Furthermore, 20.46% of animals
solved anestrus by using pigeon faeces (10–20mg.) with flour (Kartikiyanand 1996; Sah 1999).
Tomaintain the estrus cycle regular, six Fowl’s egg for oneweekwere provided to the animals
and 12.67% of these overcome the problem. Also, this technique was previously suggested
from, Mandal (1999) and Sah (1999) by using raw eggs. Finally, 16.30% of buffaloes solved
anestrus following exercise and 3.84% by feeding 5–7 kg Maili (sugarcane juice supernatant)
for three days during the winter season to induce the estrus in buffalo cows.
Conclusions
Summer anestrus is one among themajor obstacles hindering the reproductive efficiency in
buffalo and causing huge economic losses to the buffalo breeders as well as dairy industry.
Buffaloes, during the summer show poor reproductive performance characterized by silent
estrus and conception failure. Various environmental, nutritional endocrine and manage-
ment factors are responsible for triggering this condition. High temperature and humidity
together with increase day length alters the endocrine milieu resulting in poor estrus signs
and failure of conception. A good and sound management is the best approach to tackle
the summer infertility while other interventions like hormonal treatments can be employed
with varying success. Attempts should be made to identify effective hormonal regimes for
good CR rather than better induction of estrus in the summer affected buffaloes.
References
Abou-Zeina HAA, Hassan SG, Sabra HA, Hamam AM. 2009. Trials for elevating adverse effect of
heat stress in buffaloes with emphasis on metabolic status and fertility. Glob Vet. 3:51–62.
Acharya RM. 1988. The buffalo: dairy, draught and meat animal of Asia. Proceedings of the Second
World Buffalo Congress, Vol 2, PartI; New Delhi, India. p. 3–17.
Barile VL. 2005. Improving reproductive efficiency in female buffaloes. Livestk Prod Sci. 92:83–194.
Beg MA, Totey SM. 1999. The oestrous cycle, estrus behaviour and the endocrinology of the
oestrous cycle in the buffalo (Bubalus bubalis). Anim Breed Abstr. 67:329–337.
Bughio S, Shahani AK, Mirani AH, Moriani AA, Oad FC, Bughio BA. 2000. Seasonal trend of calving
and subsequent service period in buffaloes. Pak J Biol Sci. 3:2169–2170.
Chaudhry RA. 1988. Recent advances in female reproduction. Proceedings of Second World Buffalo
Congress; Dec; Delhi, India. Vol. II, Part I. p. 225–228.
Cockrill WR. 1993. Developing the water buffalo: a decade of promise. Buffalo J. 9:1–11.
De Rensis F, Lopez-Gatius F. 2007. Protocols for synchronizing estrus and ovulation in buffalo
(Bubalus bubalis): a review. Theriogenology. 67:209–216.
De Rensis F, Scaramuzzi RJ. 2003. Heat stress and seasonal effects on reproduction in the dairy
cow: a review. Theriogenology. 60:1139–1151.
Desai MC, Thakkar TP, AminDarshona R, Janakiraman J. 1982. A note on serum copper andiron in
Surti-buffalo in relation to reproduction and gonadotrophins. Indian J Anim Sci. 52:443–444.
Di Palo R, Ariota B, Zicarelli F, De Blasi M, Zicarelli G, Gasparrini B. 2009. Incidence of pregnancy
failures in buffaloes with different rearing system. Ital J Anim Sci. 8(2):619–621.
FAOSTAT. 1997. http://faostat.fao.org
BIOLOGICAL RHYTHM RESEARCH 7
FAOSTAT. 2007. http://faostat.fao.org
Gangwar PC. 1980. Climate and reproduction in buffaloes a review. India J Dairy Sci, Bangalore. 33
(4):419–426.
Gordon I. 1996. Introduction to controlled reproduction in buffaloes. In: Gordon I, editor.
Controlled reproduction in cattle and buffaloes. Oxon: CAB International; p. 432–449.
Gupta SK, Das GK. 1999. Ovarian activity and uterine involution in post parturient buffalo: effectof
suckling – an overview. J Remount Vet Corps. 38:135–142.
Gupta SK, Dhoble RL. 1988. Response of subestrus rural buffaloes to PGF2a analogue in relation to
levels of triiodothyronin (T3), tetraiodothyronin⁄ thyroxine (T4) and progesterone. Proceedings
of Second WorldBuffalo Congress, Vol. III Part I; Dec 12–16; New Delhi, India. p. 1162–1164.
Harjit K, Arora SP. 1982. Influence of level of nutrition and season on estrous cycle and fertility in
buffaloes. Buffalo Bull. 1:15.
Jain GC. 1988. Hormonal profiles in anestrus rural buffaloes. Proceedings of Second World Buffalo
Congress, Vol. 2, Part 1; New Delhi, India. p. 39.
Jainudeen MR. 1988. Reproduction problems of buffaloes in the world. Proceedings of Second
World Buffalo Congress, Vol. 2, Part 1; Dec 12–16; New Delhi, India. p. 89–196.
Jainudeen MR. 1989. Reproduction in the buffalo. In: Noakes DE, Parkinson TJ, England GCW, editors.
Arthur’s veterinary reproduction and obstetrics. 8th ed. India: Saunders Harcourt; p. 789–800.
Jainudeen MR, Hafez ESE. 2000. Reproductive cycles in cattle and buffaloes. In: Hafez ESE, Hafez B,
editors. Reproduction in farm animals. 7th ed. Baltimore (Maryland): Lea and Febiger; p. 297–314.
Janakiraman K, Desai MC, Anim DR, Sheth AR, Moodbird SB, Wadadekar KB. 1980. Serum gonado-
tropin levels in buffaloes in relation to phases of oestrous cycle and breeding periods. Indian
J Anim Sci. 50:601–606.
Kartikiyanand C. 1996. Indigenous technical knowledge of the tribes in agriculture. J Extn Edu. 7
(2):1417–1421.
Khodaei Motlagh M. 2003. Study of some effective factors in reproductive performance of Iranian
Holstien cows thesis animal physiology. Iran: Tehran University.
Madan ML. 1984. Studies on physiology of buffaloes and cattle. Summary research report. Haryana
(India): Animal Physiology, National Dairy Research Institute, Karnal (ICAR).
Mandal. 1999. Awareness about ethnoveterinary medicines of livestock feeding and healthcare
among dairy farmers in Bankura District (WB) [M Sc. Thesis]. Karnal: NDRI.
Marai IFM, Habeeb AAM, Gad AE. 2002. Rabbit’s productive, reproductive and physiological traits
as affected by heat stress (a review). Livestk Prod Sci. 78:71–90.
Misra MS, Sengupta BP. 1965. Climatic environment and reproductive behaviour of buffaloes.
Observations on semen quality of buffalo maintained under two different housing conditions.
Indian J Dairy Sci. 18:130–133.
Misra MS, Sengupta BP, Roy A. 1963. Physiological reactions of buffalo cows maintained in two
different housing conditions during summer months. Indian J Dairy Sci. 16:203–215.
Moss RJ. 1993. Rearing heifers in the subtropics: nutrient requirements and supplementation.
Tropical- Grasslands. 27:238–249.
Neglia G, Gasparrini B, Palo RD, Rosa CD, Zicarelli L, Campanile G. 2003. Comparison of pregnancy
rates with two estrussynchronization protocols in Italian Mediterranean buffalo cows.
Theriogenology. 60:125–133.
Neglia G, Rendina M, Balestrieri A, Grasso FL, Potena A, Russo I, Zicarelli L. 2009. Influence of a
swimming-pool on fertility in buffalo species. Ital J Anim Sci. 8(2):637–639.
Pandey MD, Roy A. 1966. Vitamin A and carotene status of domestic ruminants and the effects of
seasons on vitamin A storage in buffaloes. Indian Vet J. 43:613–621.
Pant HC, Barot LR, Dugwekar YG, Kasiraj R, Prabhakar JH. 2002. Hormonal induction of estrus in
anestrus buffaloes. Indian J Anim Reprod. 23:32–34.
Paraneswaran M, Thakkar TP, Janakiraman K. 1983. Activity in relation to ovarian structures and
breeding seasons in the water buffaloes. Indian J Anim Reprod. 4:5–8.
Qureshi MS, Habib G, Nawab G, Siddiqui MM, Ahmad N, Samad HA. 2000. Milk progesterone
profiles in various reproductive states in dairy buffaloes under field conditions. Proceedings of
National Science Council; Taipei, Taiwan. Vol. 24. p. 70–75.
8 K. VIJAYALAKSHMY ET AL
Randhawa CS, Randhawa SS, Singh N, Sidhu SS. 2004. Copper supplementation and fertility
response in anestrus buffaloes – a clinical trial. Indian J Anim Reprod. 25:41–42.
Razdan MN. 1988. Buffalo performance in relation to climatic environment. Proceedings of Second
World Buffalo Congress, Vol 2, Part 1; Dec 12–16; New Delhi, India. p. 173–186
Roy A, Raizada BC, Tiwari RBL, Pandey MD, Yadav PC, Sengupta BP. 1968. Effect of management on
fertility of buffalo cows bred during summer. Indian J Vet Sci. 38:554–560.
Sah. 1999. An analysis of dairy animals breeding and management practices in hill zone of U.
P. A gender perspective [Ph.D. Thesis (Unpublished)]. Karnal: NDRI.
Sarvaiya NP, Mehta VM, Patel AVC. 1993. Blood serum oestradiol-17b and progesterone around
parturition in Surti buffaloes. Indian J Anim Sci. 63:294–295.
Shah SNH. 1990. Prolonged calving intervals in Nilli-Ravi buffalo [Ph.D. Thesis]. India: National Dairy
Research Institute (NDRI).
Sheth AR, Wadadekar KB, Moodbidri SB, Janakiraman K, Paramesh M. 1978. Seasonal alteration in
the serum prolactin and LH levels in the water buffaloes. Curr Sci. 47:75–77.
Singh AP, Sah RS, Singh RB, Akhtar MH, Roy GP, Singh C, Kunj V. 2006. Response of mineral
mixture, prajana and gnrhon serum biochemical constituents and conception rate in anestrus
buffalo. Indian J Anim Reprod. 27:51–54.
Singh B, Chaudhry KC. 1992. Plasma hormonal and electrolyte alterations in cycling buffaloes
(Bubalus bubalis) during hot summer months. Int J Biometereol. 36:151–154.
Singh G, Singh GB, Sharma RD, Nanda AS. 1983. Experimental treatment of summer anestrus in
buffaloes with norgestomet and PRID. Theriogenology. 19:323–329.
Singh J, Madan ML. 1989. Hyperprolactinaemia: a possible cause of summer anestrus in buffaloes.
Proceedings of National Symposium of Applied Reproduction in Farm Animals and 8thnational
Convention of ISSAR; Nov 10–12; Anand.
Singhal SP, Dhanda OP, Razdan MN. 1984. Some managemental and therapeutic approaches in
the treatment of physiological infertility of water buffaloes (Bubalus bubalis). Proceedings of
10th International Congress Animal Reproduction Artificial Insemination, Vol. 3; Urbana
Campaign (IL). p. 471.
Verma DN, Lal SN, Singh SP, Parkash OM, Parkash O. 2000. Effect of season on biological responses
and productivity of buffalo. Int JAnim Sci. 15:237–244.
West JW. 1999. Nutritional strategies for managing the heatstressed dairy cow. Am Soc Anim Sci
Am Dairy Sci Assoc. 2:21–35.
Wettemann RP, Tucker HA. 1974. Relationship of ambient temperature to serum prolactin in
heifers. Proc Soc Exptl Med. 146:908–911.
Yessein S, Shawki H, Bashandy MM, Essawy S, Abdallah I. 1994. Clinicopathological studies in
infertile buffaloes. Indian J Anim Reprod. 15:14–18.
Zhengkang H, Zhenzhong C, Shaohua Z, Vale WG, Barnabe VH, Mattos JCA. 1994. Rumen
metabolism, blood cortisol and T3, T4 levels and other physiological parameters of swamp
buffalo subjected to solar radiation. Procceedings of World Buffalo Congress; San Paulo, Brazil.
Vol. 2. p. 39–40.
Zicarelli L. 1994. Management under different environmental conditions. Buffalo J. 2:17–38.
Zicarelli L 1997. Reproductive seasonality in buffalo. Proceedings of Third International Course of
Biotechnology in Buffalo Reproduction; Oct 6–10; Napoli: Suppl. Bubalus Bubalis. Vol. 4. p. 29–52.