Observations on the use of progesterone intravaginally and of deslorelin STI in acyclic mares for induction of ovulation

Abstract

Summary In this clinical study, 29 acyclic mares with inactive ovaries were treated with an intravaginal device containing 1.9 g progesterone (CIDR-B) for 10 to 12 days. Mares which formed a follicle >30 mm after CIDR-B removal received a subcutaneous implant containing 1.5 mg or 2.2 mg deslorelin, a potent GnRH analog. Twelve mares were treated during the breeding season (BS), 17 during autumn and winter anestrus (AS). During fall-winter anestrus, 77 untreated patient mares served as contemporary controls. Due to the uniformity of response, data were pooled. Twenty-seven out of 29 mares responded to CIDR-B treatment with follicle growth; 22 mares were treated with deslorelin when follicles had reached 38 mm within 2.6+2.3 days after CIDR-B withdrawal and 20 mares ovulated within 2.77+1.66 days. Fifteen mares were inseminated and 10 (66.7%) became pregnant at first breeding. Half of the mares treated during AS with CIDR-B only, and not with deslorelin ovulated; in all other of those mares, the preovulatory-size follicle regressed eventually.