Reproduction in Domestic Animals

210 PS Brar and AS Nandalactating animals throughout Indian subcontinent, especiallyunder small holding farming system (Singh et al.2006). The phenomenon of suckling appears to be moreintense in zebu cows than in crossbred cows. A study onrestricted suckling revealed that zebu suckled for 36% ofthe grazing time which was significantly longer than incrossbred cows. In addition, the duration of eachsuckling bout and number of suckling bouts weresignificantly higher in zebu cows than in crossbred.The duration and frequency of cross-suckling and intersucklingdecreased with increase in age of calves, andboth behaviour variables were significantly higher forcrossbred calves than for zebu calves. Although zebucows had lower milk yield, the total duration of sucklingand preferential bonding towards their own offspringswere higher than in crossbred cows (Das 1999). Therewas no significant difference in the growth rate ofdivergent follicles between suckling restricted and sucklingnon-restricted cows (0.87 vs 0.93 mm ⁄ day, respectively).However, with 72-h suckling restriction, 94.7%postpartum cows showed signs of oestrus when comparedwith 46.6% in the control group (p < 0.05;Mahecha et al. 2003). Temporary suspension of sucklingenhanced the oestrous synchronization success in Nelorecows (Moraes et al. 2003).Studies on improving success of AI in Ongole cowsrevealed better conception rates with semen depositeddeep intrauterine (73.63%) than in body of uterus(63.79%) or mid-cervix (53.68%) (Rao and Naidu2001). Wrong time insemination (9–15%), a majorcause infertility in zebu cows, has been reported in themost developing countries including Bangladesh, Chinaand Myanmar. Further, microbial endometritis in morethan 11% zebu cows forms other factor limiting thesuccess of AI (Shamsuddin et al. 2007).Zebu cattle in tropical Asia are normally kept bysmall farmers and often under poor managementalconditions. They are prone to parasitic infestations, animportant pathological variable causing prolongedpostpartum anoestrus in zebu cattle. In a study incentral parts of India, Singh and Saxena (2006) revealedbursate worms infestation in 100% anoestrous Haryanacows. Substantially, higher proportion of these cameinto oestrus within 20 days after deworming (26% vs14% untreated cows). Ecto- and endoparasitism ishighly prevalent in zebu cows in tropical Asia. Luckily,however, they have better innate immunity against theseand other tropical diseases compared with the crossbredcattle (Chenoweth 1994). Their reproduction is, therefore,less likely to be affected by such diseases than theircrossbred counterparts.It is thus evident that the reproductive efficiency ofzebu cows could be improved through provision ofproper nutrition, management, especially during periparum,calf weaning and improved oestrous detection(Mugerwa et al. 1991).Conservation of Zebu CattleConservation of zebu cattle is very important owingto their merits of better disease resistance, thermotoleranceand crude fibre utilization than in crossbredand exotic cows. Overall incidence of clinical reproductivehealth problems was lesser in zebu than intheir crosses with exotic blood (22% vs 36%). Studiesby Mandal et al. (2005) revealed that incidence ofabortion, still birth, premature birth, retention ofplacenta, dystocia and total parturient disorders were3.16%, 2.70%, 0.45%, 7.00%, 0.90% and 14.21%,respectively. More cows suffered from parturientdisorders during winter, followed by summer, andrainy seasons. Seasons, however, appeared to have nomajor effect on mortality rate in adult zebu cattle(Prasad et al. 2004), owing perhaps to their innatetolerance to extremes of tropical temperature andhumidity. Pre-implantation zebu embryos are lessvulnerable to elevated temperature than are embryosfrom European breeds (Hansen 2004). In response tothreats of global warming, further development andpropagation of zebu cattle are vital.From the foregoing, it is evident that the zebu cattlehas been and is an integral and vital part of socioeconomiclife, especially in rural tropical Asia. However,these animals did not attract the attention of thescientists and the policy makers alike, and postpartumreproductive physiology remained unexplored and thezebu unexploited. The fact that several breeds of Asianzebu have performed better in American and Australiancontinents, emphasis is needed on studies to developstrategies to exploit the full production potential ofthese breeds within Asia too. As the postpartum periodis the key window in the entire spectrum of reproductiveprocess, much more work needs to be carried out tounderstand the physiology and the limiting factors sothat appropriate interventions to enhance fertility inzebu cattle are developed.ReferencesAbeygunawardena H, Dematawewa CM, 2004: Pre-pubertaland postpartum anoestrus in tropical zebu cattle. AnimReprod Sci 82–83, 373–387.Abeygunawardena H, Abayawansa WD, Kaduwela SC, 1992:Postpartum anostrus in cattle and buffaloes;experiences withhormonal therapy. In: Proceedings of 45th Annual Conventionof Sri Lanka Veterinary Association, Colombo, SriLanka 11–12 December 1992, pp 21.Ahuja C, Montiel F, 2004: Induction of ovulation with GnRHand PGF2 alpha in lactating Bos taurus · Bos indicus cows.Acta Vet Hung 52, 501–508.Akhtar T, Lodhi LA, Khanum SA, Rashad MA, Hussain M,2007: Improving reproductive efficiency in an artificialinsemination programme through early non-pregnancydiagnosis, management and training. 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