Ovarian follicular dynamics and pregnancy outcomes of Thai swamp buffaloes (Bubalus bubalis) submitted to ovulation-synchronization protocol with different timing of insemination.

Experiments were conducted to investigate follicular dynamics and timing of ovulation in Thai swamp buffaloes (Bubalus bubalis) and compare the pregnancy rate in buffaloes submitted to the 11-day progesterone (P4)-prostaglandin F2α (PGF2α)-equine chorionic gonadotrophin (eCG)-gonadotropin-releasing hormone (GnRH)-based protocol with different timing of insemination. In experiment 1, follicular dynamics and timing of ovulation were determined from buffaloes receiving P4-device insert from Days 0 to 11, PGF2α and eCG on Day 11, and GnRH at 48 h after P4-device removal. In experiment 2, the pregnancy rate was compared between buffaloes that were inseminated either at 72 or 96 h after P4-device removal. Ovulatory buffaloes had a greater growth rate of the dominant follicle from Day 11 to 48 h after P4-device withdrawal compared with anovulatory buffaloes (1.2 ± 0.10 vs. 0.8 ± 0.11 mm/day). The peak level of luteinizing hormone (LH) showed an increase in ovulatory buffaloes compared with anovulatory buffaloes (4.8 ± 0.46 vs. 2.5 ± 0.15 mIU/mL). The interval between P4-device removal and LH peak was shorter in ovulatory buffaloes compared to anovulatory buffaloes (79.2 ± 5.11 vs. 116.4 ± 14.54 h). The majority of the buffaloes ovulated 96 h after P4-device withdrawal (75.0%). Inseminating buffaloes 72 h after P4-device removal yielded a higher pregnancy rate than when buffaloes were inseminated 96 h after P4-device removal (71.4 vs. 44.4%). It is concluded that an optimal pregnancy rate can be achieved when Thai swamp buffaloes are bred artificially 72 h after P4-device removal, following ovulation-synchronization with the 11-day P4-PGF2α-eCG-GnRH-based protocol.