Effect of Bull Exposure on Ovarian Cyclicity in Postpartum Buffaloes

The objective of this experiment was to evaluate the effect of bull exposure on ovarian cyclicity in postpartum Murrah buffaloes. Twentyone buffaloes between the fi rst to fi fth lactation, which had calved during September and early February, were assigned at random to receive one of the following two treatments: (1) exposure to a vasectomized bull (bull exposed, BE) and (2) isolated from bull (non-exposed, NE). The animals of the BE group (n=11) were continuously exposed to a vasectomized bull, which was tethered in a semi-open shed from the 3rd to the 60th day postpartum, whereas the buffaloes of the NE group (n=10) were kept in another semiopen shed, at a distance of approximately 0.13 km. After the end of the treatment period, all the animals of the BE and NE groups were mixed together and their cyclicity was further monitored for another 30 days. Blood samples were collected from each animal at weekly intervals beginning from day 3 to day 30 postpartum, and thereafter at 4-day-intervals up to day 90 postpartum. A rise in progesterone concentration ≥1.0ng/ml for at least two consecutive samples was used as the criterion for resumption of ovulatory cycles. In each group, the animals were checked twice daily for signs of estrus by parading a teaser bull at 7:00 h and 17:00 h. Animals detected in standing estrus were further confi rmed by rectal examination before insemination at 12 and 24 h after onset of standing estrus using 0.5 ml of frozen-thawed semen of fertile bulls. Pregnancy was checked by per rectal examination at 60 days post insemination. Exposure of the buffalo cows to the vasectomized bull did not (p>0.05) alter: (1) postpartum interval to uterine involution, occurrence of fi rst behavioral estrus and ovulation or (2) the proportion of cows that resumed cycling activity compared to cows not exposed to bull. However, the incidence of silent ovulation was signifi cantly (p<0.05) lower in the BE group (57.14%) compared to the NE group (85.71%). Furthermore, the BE group of animals had a higher conception rate (p<0.05) than the NE group (81.82% versus 40.0%). We conclude that continuous exposure of postpartum buffalo cows to a vasectomized bull curtails the incidence of silent ovulation and enhances the conception rate.