การจัดการการสืบพันธุ์ด้วยโปรแกรมฮอร์โมนที่มีประสิทธิภาพสำหรับ การเหนี่ยวนำ การตกไข่และการผสมเทียมแบบกำหนดเวลา ในโคนมสาวทดแทน

Abstract

The short-term (7-day) progesterone (P4) -gonadotropin releasing hormone (GnRH) -prostaglandin F2α (PGF2α)-based synchronization and fixed-time artificial insemination (FTAI) protocol has been widely applied in dairy cattle farm for reproductive management. Although the first GnRH administration in this short-term protocol is required to induce new follicular wave initiation, only a few heifers ovulated in response to first GnRH injection. The aims of this experiment, therefore, were to 1) study the necessity of the first GnRH treatment at the time of initiation of the 7-day P4- GnRH- PGF2α-based synchronization protocol on follicular dynamics and 2) evaluate the effect of ovarian cyclicity (appearing or disappearing corpus luteum [CL] on ovary) prior to the start of ovulation synchronization on fertility in replacement dairy heifers submitted to the FlAI protocol. In experiment 1, 29 heifers were divided into three groups: control (no synchronization; n=10), No-first GnRH (n=9), and Yes-first GnRH (n=10) groups. Heifers in the control group that did not receive the 7-day P4-GnRH- PGF2α -based synchronization protocol were evaluated follicular dynamics throughout the interovulatory interval. In the Yes- and No-first GnRH groups. heifers received the 7-day P4-GnRH- PGF2α -based synchronization protocol (on day 0, controlled internal drug release device [CIDR] insert was administrated; on day 7, CIDR was removed and PGF2α was injected; and on day 9, final GnRH was injected) with (Yes-first GnRH) or without (No-first GnRH) GnRH injection on day 0. The growth and ovulation of ovarian dominant follicle (DF) was wvaluated by transrectal ultrasound scanning. Blood samples were collected from each cow in the No- and Yes- first GnRH groups to analyze plasma P4 concentrations during CIDR insert and after CIDR removal. In experiment 2, 438 heifers were divided into three groups: control (No synchronization; n=195), No-first GnRH (n=105), and Yes-first GnRH (n=138) groups. Heifers in the control group that did not receive the hormonal synchronization protocol were inseminated upon detection of estrus. Heifers in the No- and Yes-first GnRH groups that received the 7-day P4-GnRH- PGF2α -based synchronization protocol were inseminated with FTAI on day 9. Moreover, heifers in the No- and Yes-first GnRH groups were sub-divided in 2 groups according to the appearance (+CL; n=191) or disappearance CL (-CL; n=52) on day of the initiation of ovulation synchronization (day 0). In results of experiment 1, estrous and ovulation rates did not differ (P > 0.05) among the control (100.00% and 100.00%), No-first GnRH (100.00% and 88.89%), and Yes-first GnRH (90.00% and 90.00%) groups. Heifers in the No- and Yes-first GnRH groups had a greater (P < 0.05) DF diameter at ovulation (14.55 ± 0.77 mm and 14.45 ± 0.46 mm), compared with cows in the control group (12.05 ± 0.22 mm). The plasma P4 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, estrous rate and pregnancy rates at days 32 and 60 after AI did not differ among heifers in the control (65.13%, 64.62%, and 62.56%, respectively), No-first GnRH (62.86%, 62.86%, and 58.10%, respectively), and Yes-first GnRH (60.87%, 60.87%, and 55.07%, respectively) groups. In the No-first GnRH, heifers that appeared a CL ( +CL) had greater (P < 0.01) estrous rate and pregnancy rates at days 32 and 60 after AI, compared with cows that disappeared a CL (-CL) on their ovaries (73.39% vs. 20.69%, 72.48% vs. 17.24%, and 65. 14% vs. 17.24%, respectively). In the Yes-first GnRH group, estrous rate, and pregnancy rates at days 32 and 60 after AI were greater (P < 0.01) in heifers having a CL (+CL) than cows that appeared a CL (-CL) on their ovaries (79.27% vs. 26.09%, 74.39% vs. 21.74%, and 68.29% vs. 21.74%, respectively). In conclusion, these results indicated the 7-day P4-GnRH-PGF2α based protocol without GnRH treatment at the initiation of ovulation synchronization had no negative effects on ovarian follicular development and fertility in replacement dairy heifers. Furthermore, replacement dairy heifers that appeared ovarian cyclicity prior to the start of FTAI with the 7-day P4-GnRH-PGF2α -based protocol had an increase in the rate of pregnancy.