OVARIAN FOLLICULAR WAVE SYNCHRONIZATION AND INDUCTION OF OVULATION INPOSTPARTUM BEEF-COWS

An experiment was designed to evaluate a) the effect of a progesterone -estradiol combined treatment on ovarian follicular dynamics in postpa rtum beef cows, and b) ovulation and the subsequent luteal activity af ter short-term calf removal and GnRH agonist treatment. Multiparous An gus cows (25 to 40 d after calving) were assigned to the following tre atments: 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 be ta 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 gr oups) 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 concentr ations 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 t o 5), the variability was less (P<0.05) in the CIDR+E-17 beta group. T he proportion of cows ovulating 24 to 48 h after GnRH administration t ended (P=0.08) to be higher in cows from CIDR+E-17 beta group (8/9) th an in those of CR (5/8) or CIDR (6/9) groups, respectively and was ass ociated with a higher proportion (P<0.05) of CIDR+E-17 beta treated co ws (9/9) that had a dominant follicle in the growing/early static phas e at the time of GnRH treatment compared to the other GnRH treated gro ups (5/8, and 4/9 for CR and CIDR groups, respectively). Two CR cows o vulated 0-24 h after GnRH and only one Control cow ovulated the day be fore the time of GnRH administration. Cows pretreated with progesteron e had longer (P<0.05) luteal lifespan (CIDR, 14.5 +/- 0.7, CIDR+E-17 b eta, 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 o vulation rate with normal luteal activity in postpartum beef cattle. ( C) 1998 by Elsevier Science Inc.