Synchronization of ovulation in beef cows (Bos indicus) using GnRH, PGF2alpha and estradiol benzoate.

摘要

The objective of this study was to evaluate protocols for synchronizing ovulation in beef cattle. In experiment 1, Nelore cows (Bos indicus) at random stages of the oestrous cycle were assigned to 1 of the following treatment groups: (1) GP controls(non-lactating, n = 7) received GnRH agonist (Conceptal, day 0) and PG (Lutalyse, day 7); (2) GPG (non-lactating, n = 8); and (3) GPG-L (lactating, n = 9) cows were given GnRH (day 0), PG (day 7) and GnRH again (day 8, 30 h after PG). A new follicular wave was observed 1.79±0.34 days after GnRH in 19/24 cows. After PG injection, ovulation occurred in 19/24 cows (6/7 GP, 6/8 GPG, 7/9 GPG-L). Most cows (83.3%) exhibited a dominant follicle just before PG injection, and 17/19 ovulatory follicles were froma new follicular wave. There was a more (P<0.01) precise synchrony of ovulation (within 12 h) in cows that received a second dose of GnRH (GPG and GPG-L) than controls (GP, ovulation within 48 h). In experiment 2, lactating Nelore cows with a visible corpus luteum (CL) by ultrasonography were allocated to 2 treatment groups: (1) GPE (n = 10) received GnRH agonist (day 0), PG (day 7) and oestradiol benzoate (EB; day 8, 24 h after PG injection); (2) EPE (n = 11), received EB (day 0), PG (day 9) and EB (day 10, 24 h after PG injection). Emergence of a new follicular wave was observed 1.6±0.31 days after GnRH (group GPE). After EB injection (day 8) ovulation was observed at 45.38±2.03 h in 7/10 cows within 12 h. Emergence of a new follicular wave was observed later (P<0.001) in EPE (4.36±0.31 days) than in GEP (1.6±0.31 days). After the second EB injection (day 10) ovulation was observed at 44.16±2.21 h within 12 (7/11 cows) or 18 h (8/11 cows). All 3 treatments were effective in synchronizing ovulationin beef cows. However, GPE and, particularly, EPE treatments offer a promising alternative to the GPG protocol in timed AI of beef cattle, due to the low cost of EB compared with GnRH agonists.