Session IV: Reproduction and Physiology Determination of cyclicity in yak (Poephagus grunniens L.) through plasma progesterone estimation

An attempt was made to determine the cyclicity in yak through plasma progesterone estimation during breeding season as well as non-breeding season because silent or non-detected estrus is very common in this species. Blood samples were collected from yak (n = 8) during peak breeding season (July to November) and from the same animals in non-breeding season (February to March) at a two-day interval for 30 days. Progesterone in plasma was estimated using radioimmunoassay. During breeding season, a high proportion (68%) of heats went unnoticed as confirmed by plasma progesterone profiles which indicated that silent or weak estrus was prominent in yak cows. The common signs of estrus were, followed and mounted by male yak, standing to be mounted, frequent urination, rising of tail, swelling of vulva, congestion of vulvar mucous membrane, restlessness and alertness, loss of appetite. But no bellowing was observed in any yak at estrus. The plasma progesterone at estrus was very low and reached a peak at day 15 of the cycle and thereafter declined rapidly from four days before estrus to basal levels at estrus. During non-breeding season, although no behavioral symptom of estrus was found in any yak cow, three animals were found to be cycling as confirmed by cyclic change in plasma progesterone concentration in those animals. Our observation throws every doubt on the so called “seasonal breeding pattern” of yak and warrants more detailed investigation.