Induction of estrus in suckled female yaks (Bos grunniens) and synchronization of ovulation in the non-sucklers for timed artificial insemination using progesterone treatments and Co-Synch regimens

The objectives of the present study were to evaluate the induction of estrus and fertility in yak cows treated with Co-Synch regimens or progesterone (P4). In Experiment 1, postpartum suckled yaks were assigned to three treatments: (1) A (n = 28), insertion of an intravaginal device containing P4 (CIDR) on Day 0, PGF2α (i.m.) on Day 6 and PMSG (i.m.) at the time of CIDR removal on Day 7 (P4-PGF2α-PMSG); (2) B (n = 21), PGF2α (i.m.) on Day 6 and PMSG on Day 7; (3) C (n = 26), control group. Seven yak bulls were grazed with the cows for natural breeding. Rate of estrus within 96 h of the end of treatment was greater (P < 0.05) in A (100.0%) than in B (28.6%) or C (0.0%). First service conception rate (CR) determined by serum P4 on Day 21 after breeding was greater (P < 0.05) in A (78.6%) than in B (22.2%). Also, pregnancy rate (PR) during the breeding season was greater (P < 0.05) in A (82.1%) than in B (19.0%) and C (7.7%). In Experiment 2, non-suckled yaks that calved in previous years but not in the current year were assigned to three treatments: (1) A (n = 31), GnRH (i.m.) on Day 0, followed by PGF2α on Day 7 and timed artificial insemination (TAI) concurrently with GnRH treatment on Day 9 (Co-Synch regimen); (2) B (n = 50), a CIDR device for 7 days plus PGF2α and PMSG at the time of CIDR withdrawal on Day 7 and TAI on Day 9 (P4-PGF2α-PMSG); (3) C (n = 50), yak cows were artificially inseminated at spontaneous estrus. Frozen semen of Holstein and Jersey were used for insemination in Experiment 2. The CR assessed by rectal palpation 35 days after TAI was not different in A (22.6%), B (30.0%) and C (33.3%), but PR was greater in A and B than in C, when based on those cows presented for estrous synchronization programs. It is concluded that P4-PGF2α-PMSG protocol could efficiently induce estrus and result in an acceptable pregnancy rate in postpartum suckled yak cows. This technique and Co-Synch regimen can be applied successfully for TAI of non-suckled yak cows.