Ovarian follicular wave synchronization and induction of ovulation in postpartum beef cows

An experiment was designed to evaluate a) the effect of a progesterone-estradiol combined treatment on ovarian follicular dynamics in postpartum beef cows, and b) ovulation and the subsequent luteal activity after short-term calf removal and GnRH agonist treatment. Multiparous Angus cows (25 to 40 d after calving) were assigned to the following treatments: untreated (Control, n=9); short term calf removal (CR, n=8); progesterone (CIDR, n=9) and progesterone plus estradiol-17 beta (CIDR+E-17 beta, n=9). Progesterone treatment (CIDR) lasted 8 d and the day of device insertion was considered as Day 0. Cows in the CIDR+E-17 beta group also received an im injection of 5 mg of E-17 beta on Day 1. On Day 8, calves were removed for 48 h (CII CIDR and CIDR+E-17 beta groups) and 6 h before the end of calf removal these cows also received an im injection of 8 mu g of Busereline (GnRH). Anestrus was confirmed in all cows by the absence of luteal tissue and progesterone concentrations below 1 ng ml(-1) at the beginning of the experiment. Although mean (+/-SEM) interval from the beginning of the experiment (Day 0) to wave emergence did not differ (P>0.05) among treatment groups(Control, 1.9 +/- 1.0, range -2 to 7 d; CR 3.9 +/- 0.7, range 0 to 6 d; CIDR, 2.8 +/- 0.5, range 0 to 4 d and CIDR+E-17 beta, 4.1 +/- 0.2, range 3 to 5), the variability was less (P<0.05) in the CIDR+E-17 beta group. The proportion of cows ovulating 24 to 48 h after GnRH administration tended (P=0.08) to be higher in cows from CIDR+E-17 beta group (8/9) than in those of CR (5/8) or CIDR (6/9) groups, respectively and was associated with a higher proportion (P<0.05) of CIDR+E-17 beta treated cows (9/9) that had a dominant follicle in the growing/early static phase at the time of GnRH treatment compared to the other GnRH treated groups (5/8, and 4/9 for CR and CIDR groups, respectively). Two CR cows ovulated 0-24 h after GnRH and only one Control cow ovulated the day before the time of GnRH administration. Cows pretreated with progesterone had longer (P<0.05) luteal lifespan (CIDR, 14.5 +/- 0.7, CIDR+E-17 beta, 13.9 +/- 0.6 d) than those not treated with CIDR (Control, 5, CR, 4.0 +/- 0.4). We conclude that progesterone plus estradiol treatment results in tightly synchronized wave emergence and high GnRH-induced ovulation rate with normal luteal activity in postpartum beef cattle. (C) 1998 by Elsevier Science Inc.