Follicular and Luteal Dynamics During Natural and Induced Estrous Cycle in Arunachali Yak (Bos grunniens)

To study follicular growth pattern and luteal dynamics during natural and induced estrous cycle in Arunachali Yak maintained at the Nyukmadung farm of ICAR-NRC on Yak of Arunachal Pradesh. A total of 36 animals of apparently healthy cyclic female yaks of first to fourth parity and free from any post parturient complications, maintained under intensive system of rearing were selected for the study and equally divided into two groups. Female yak with natural oestrus was placed in Group-I and the female yak subjected to Double Ovsynch protocol were placed in Group-II. Transrectal-ultrasonography was performed daily for one oestrous cycle to monitor the follicular growth pattern and Luteal dynamics. Three wave patterns were observed in natural oestrus and four wave patterns were observed in induced oestrous female yak. The common follicular wave pattern in Arunachali Yak was two wave pattern (66.67%) in natural oestrus and three wave pattern (77.78%) in induced oestrus. The overall mean oestrous cycle length in natural oestrous (Group I) and induced oestrous (Group II) female yak was found to be 20.00±0.86 and 22.50±0.57 daysrespectively.Two follicular wave patterns in natural oestrus and three follicular wave patterns in induced oestrus was the most common in Arunachali Yak. The length of first follicular wave was found to be maximum in both natural and induced oestrous. The length of follicular wave decreases successively as the number of follicular waves increases in Arunachali Yak. The size of Corpus Luteum was found significant difference in between the group.