Reproduction in Domestic Animals

220 BS Prakash, M Sarkar and M Mondalduring night times. Sarkar and Prakash (2005c) alsoobserved that the overall plasma prolactin levels duringday as well as night time were found to be more in nonbreedingmonth than the corresponding time in breedingmonth. This marked increase of prolactin level in nonbreedingseason may be stress related and associatedwith harsh environmental condition particularly lowtemperature as well as nutritional stress during the nonbreedingseason. The relationship between prolactin andmelatonin secretion in blood plasma during breeding(November) and non-breeding (February) months wasinvestigated in yaks by Sarkar and Prakash (2005c). Thepositively correlated (0.8 in breeding season and 0.7 innon-breeding season) circadian rhythms of plasmamelatonin and prolactin is not clearly understood.Tindal (1974) reported that melatonin profoundlymodulates prolactin release from the adenohypophysis.However, different species interpret the pineal gland’shormonal signal in a fundamentally different manner.This preliminary investigation opens the gates forresearchers to unravel the interrelationship of thetwo hormones for more comprehensive and detailedinvestigation.Timing of ovulation and plasma LH in yakYaks ovulated at 30.5 ± 0.8 h (28–34 h) after theonset of spontaneous oestrus. Preovulatory LH surgeoccurred 3.0 ± 0.7 h after the commencement ofoestrus signs with the surge lasting 7.3 ± 0.6 h. Ovulationtook place 20.3 ± 1.0 h after LH surge (18–26 h)(Sarkar and Prakash 2005a).Hormone concentrations during pregnancy and periparturientperiod in yakProgesterone profiles were similar in pregnant and nonpregnantyaks up to 14 days after oestrus; however, inpregnant yaks concentrations were significantly higheron day 19 and tended to increase gradually thereafter.Plasma progesterone concentrations decreased rapidlyon day 120, then increased to reach a maximum level onday 210. Concentrations decreased again 20 days beforeparturition reaching basal levels at parturition. Oestradiol-17blevels in plasma and milk increased graduallyuntil day 23 after conception, decreased abruptly on day60, and increased again to reach a maximum level atparturition. Oestradiol concentrations decreased againafter parturition to reach similar levels as measuredduring mating (Yu et al. 1993).Profiles of progesterone, cortisol and 13,14-dihydro-15-keto-PGF 2a (PGFM) in blood plasma of yaks duringperi-parturient period were determined (Sarkar et al.2007b,c). Plasma PGFM level showed an increasingtrend beginning day 4 prior to parturition (0.73 ± 0.16ng ⁄ ml) and increased steeply thereafter to reach a peaklevel (17.16 ± 1.31 ng ⁄ ml) on the day of parturition.The levels, then, declined sharply on day 1 post-partumto reach 1.20 ± 0.40 ng ⁄ ml and thereafter declinedgradually over the days to reach 0.28 ± 0.09 ng ⁄ ml onday 20 post-partum and this level was maintained withfluctuation within narrow limits thereafter till conclusionof the blood sampling on day 90 post-calving.Plasma cortisol level showed an increasing trend beginningday 2 prior to parturition (2.36 ± 0.65 ng ⁄ ml) andincreased steeply thereafter to reach a peak level(26.65 ± 5.28 ng ⁄ ml) on the day of parturition. Thelevels, then, declined gradually over the days andreached 2.36 ± 0.25 ng ⁄ ml on day 3 post-partum, andthis level was maintained with fluctuation within narrowlimits thereafter till conclusion of the blood sampling onday 7 post-calving. The plasma progesterone concentrationon day 7 before parturition was high(2.10 ± 0.10 ng ⁄ ml). The hormone concentrationdecreased gradually followed by an abrupt fall on theday of parturition (0.24 ± 0.04 ng ⁄ ml).Endocrine Biotechniques to Enhance FertilitySilent or non-detected oestrus is one of the majorcontributory factors in both yak and mithun reproductionleading to poor reproductive efficiency in theseanimals (Sarkar and Prakash 2005a; Mondal et al.2006g).Synchronization of oestrus using PGF 2a in mithunsWe tried synchronization of oestrus using doubleinjection of PGF 2a at 11 days apart in cyclic mithuncows. Plasma LH characteristics and time of ovulationin respect to LH peak and onset of oestrus in mithuncows synchronized for oestrus with PGF 2a are presentedin Table 1. All the cyclic animals that were subjected tooestrus synchronization using PGF 2a responded to thetreatment. The intensity of oestrus in the mithun cowssynchronized with double injection of PGF 2a wascomparable to that of spontaneous oestrus (MondalM, Rajkhowa C, and Prakash BS., unpublished data).Synchronization of oestrus using CIDR in mithunsExperiments were conducted to synchronize oestrususing CIDR in cyclic and post-partum mithun cows. Inboth categories of animal, synchronized oestrus usingCIDR showed more prominent behavioural signs thanspontaneous heat (unpublished data). More interestingly,application of CIDR on day 45–50 after parturitioninduced first post-partum oestrus immediatelyafter uterine involution (day 53–58 post-parturition).Unlike other bovines, mithun cows exhibit firstpost-partum oestrus at approximately day 102 ± 19.6post-partum.Table 1. Plasma LH characteristics and timing of ovulation inmithuns subjected to two injection of PGF 2a at 11 days apart foroestrus synchronizationParameters Mean ± SEM RangeHighest LH peak concentration (ng ⁄ ml) 12.54 ± 1.37 7.34–22.65Duration of LH surge (h) 14.76 ± 1.47 10–19Time from:Second PGF 2a injection to onset of oestrus 43.52 ± 5.93 36–58Onset of oestrus to onset of LH surge (h) 2.45 ± 0.43 1.5–3.25Onset of oestrus to ovulation (h) 33.95 ± 1.41 27–39After end of LH surge to ovulation (h) 20.45 ± 0.89 17–24After end of LH surge to ovulation (h) 20.45 ± 0.89 17 to 24Ó 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag