การเปรียบเทียบความสมบูรณ์พันธุ์ในแม่โคเนื้อที่ได้รับโปรแกรมฮอร์โมนระยะสั้นเพื่อกำหนดเวลาการผสมเทียม

Abstract

The short-term progesterone (P4)-gonadotropin releasing hormone (GnRH)-prostaglandin F2α (PGF2α)-based synchronization and fixed-time artificial insemination (FTAI) protocol has been widely applied in beef cattle farm for reproductive management; therefore, an increase in the efficiency of ovulation synchronization with pregnant mare serum gonadotropin (PMSG) treatment may improve ovarian follicular growth and fertility in beef cows. The aim of this study was to evaluate the effect of PMSG treatment given during 7-day P4-GnRH-PGF2α-based synchronization protocol on ovarian follicular dynamics, estrous rate, and pregnancy rate in beef cows. In experiment 1, 30 cows were randomized into 3 groups. Control group (n=10), cows were received controlled internal drug release device (CIDR) insert for 7 days (Day 0 to Day 7) concurrent with first injection of GnRH. On the day of CIDR removal (Day 7), cows were received PGF-a and cows received second injection of GnRH at Day9. PMSG3 group (n=10), cows were received CIDR insert for 7 days (Day 0 to Day 7) concurrent with first injection of GnRH. Three day later (Day 3), cows received 400IU of PMSG. On the day of CIDR removal (Day 7), cows were received PGF-a and cows received second injection of GnRH at Day9. PMSG4 group (n=10), cows were received CIDR insert for 7 days (Day 0 to Day 7) concurrent with first injection of GnRH. Four day later (Day 4), cows received 400IU of PMSG. On the day of CIDR removal (Day 7), cows were received PGF2α and cows received second injection of GnRH at Day9. The growth and ovulation of ovarian dominant follicle (DF) was evaluated by transrectal ultrasound scanning. Blood samples were collected from each cow to analyze plasma P4 concentrations. In experiment 2, 256 cows were divided into two groups: control group (n=151) and synchronization group (n=105). Cows in the control group that did not receive the hormonal synchronization protocol were inseminated upon detection of estrus. Cows in the synchronization group that received the effective synchronization protocol from experiment 1 were inseminated with FTAI on day 9. All inseminated cows were diagnosed as pregnant on day 30 post-insemination. In results of experiment 1, ovulation rate was greatest in the PMSG4 group (90.0%) compared with the control group (40.0%) but was not different when compared with the PMSG3 (70.0%; P < 0.05). Cows in the PMSG3 and PMSG4 groups had a greater DF growth rate from the day of follicular wave emergence to the day of ovulation (1.31 ± 0.08 and 1.38 ± 0.13 mm/day), compared with cows that did not receive PMSG treatment (0.71 ± 0.08 mm/day; P < 0.05). The diameter of DF at ovulation was larger (P < 0.05) in cows that received PMSG on days 3 and 4 (13.73 ± 0.67 and 14.01 ± 0.67 mm) than cows that did not receive PMSG (9.83 ± 0.46 mm). The plasma P, concentrations during CIDR insert (> 1.00 ng/ml) and after CIDR removal (< 1.00 ng/ml) did not differ among treatment groups (P > 0.05). In results of experiment 2, cows that exhibited natural estrus and AI had greater (P <0.05) pregnancy rates, compared with cows that synchronized ovulation and FTAI (45.7 vs. 33.3%). In conclusion, these results highlighted a beneficial efiect of PMSG treatment during 7-day P4-GnRH-PGF2α -based synchronization protocol not only on ovarian follicular growth but also on the retumn to estrous rate in beef cows submitted to the FTAI protocol.