Reproduction in Domestic Animals

Reproduction Augmentation in Yak and Mithun 219(a)Estradiol-17b and totalestrogen (pg/ml)403020100E2TE(b)4.5 P4 TE4.03.53.02.52.01.51.00.50.0Progesterone (ng/ml)E2403020100Estradiol-17b, total estrogen(pg/ml)–24–18–12 –60 6 11 17 23 29Periestrous period (h)–6 –4 –2 0 2 4 6 8 10 12 14 16 18 20Days of estrous cycleFig. 2. Mean (±SEM) plasma oestradiol-17b (E2) and total oestrogen (TE) profiles of mithun cows during peri-oestrous period. Blood sampleswere collected hourly intervals for 24 h prior to onset of oestrus, at 15-min intervals for 9 h post-onset of oestrus and thereafter at 2 h intervals till31 h post-onset of oestrus (a). Mean plasma E2, TE and progesterone (P4) profiles during the different days of oestrous cycle in mithun cows(n = 12). Blood samples were collected daily for the entire cycle (b)LH (ng/ml)1086420LHProgesteroneOvulation0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40Hours after the onset of estrus1.000.750.500.250.00Fig. 3. Changes in the plasma LH and progesterone profile (mean ±SEM) in mithun cows (n = 12) after onset of oestrus. Blood sampleswere collected at 15 min intervals after the initial expression of heatsymptoms by the mithuns for 9 h period and thereafter at an intervalof 2 h till 4 h post-ovulation. Ovulation was confirmed by rectalpalpation at 2 h intervalsafter the onset of oestrus and 18.63 ± 0.35 h after theend of LH surge (Fig. 3).Seasonal breeding pattern in yaks and associatedendocrine changesYaks are considered seasonal breeders. However, informationabout the breeding season is rather conflicting.The onset and the end of the breeding season areaffected by ecological factors such as climate, grassgrowth, latitude and altitude. Following their longperiod of deprivation and weight loss over the winter,the female yaks come into the breeding season whentemperature and humidity start to rise, and grass beginsto grow which also improves their body condition. InWest Kameng and Tawang districts of ArunachalPradesh in India, the breeding season reaches its peakin July and August when temperature is at its highestand grass growth is at its best and lasts up to November.Sarkar et al. (2006b) estimated plasma progesterone,total oestrogen and oestradiol-17b profile during breeding(July to November) and non-breeding season(February to March) in yak. Plasma progesterone wasvery low (£0.2 ng ⁄ ml) at oestrus, thereafter started toProgesterone (ng/ml)rise with a sharp increase during the late luteal phaseand reached a peak on day 15–16 of the cycle, decliningrapidly thereafter to basal levels at oestrus.During non-breeding season, in 50% (4 ⁄ 8) of theanimals studied, plasma progesterone level was at basallevel as anticipated. However, cyclic changes in plasmaprogesterone were seen in three yaks while the plasmaprogesterone level stayed high throughout the samplingperiod in one animal. There were clear indications ofcyclic luteal activity in a large proportion of animalseven during the non-breeding season, although oestrussymptoms were not exhibited (Sarkar et al. 2006a). Inthe same study, plasma total oestrogen and oestradiol-17b concentrations were high at oestrus and thendeclined to basal level on day 2 of the cycle and anothersmall elevation was found between days 8 and 12 of thecycle (Sarkar et al. 2006a). This elevation of thehormones suggests the possibility of additional follicularwaves in yaks.Circadian rhythmicity in circulatory melatonin concentrationswas exhibited with low concentrations duringdaytime and high during night in both the periodsunder investigation. Similar observations have beenrecorded in cattle (Berthelot et al. 1990), buffalo(Borghese et al. 1994), sheep (Kennaway et al. 1977)and goats (Kloren and Norton 1995). A circadianrhythmicity of prolactin release was also seen with amaximum mean concentration at 04:00 h and a minimumat 14:00 h in breeding season and with a maximumvalue at 00:00 h and a minimum at 12:00 h in nonbreedingmonth. The observations on diurnal prolactinpattern in yaks seems to be in sharp contrast to thoserecorded in cattle and buffaloes where higher prolactinconcentrations have been recorded during daytime(Singh and Madan 1993; Gustafson 1994). Diurnalrhythmicity in hormonal or biochemical constituents isinfluenced by many factors including metabolic rate,nutrition and environmental conditions. Positive relationshipof prolactin secretion to stress related situationsis also well known (Raud et al. 1971; Tucker 1971).Under extremely cold conditions at night, yaks areexposed to greater stress. The condition is reversedduring the daytime, under the influence of sunlight. Thismay be the reason for higher prolactin concentrationÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag