Medroxyprogesterone Acetate: MATERIALS AND METHODS(1)
Animals and Procedures: Experiment 1
Care and treatment for experimental animals was carried out according to guidelines issued by the Canadian Council on Animal Care. Fourteen sexually mature, clinically healthy, cyclic Western white-faced ewes were used in the study, which was conducted from September to November. Estrus was initially synchronized in 24 ewes by a 14-day treatment with progestogen-releasing intravaginal sponges (MAP, 60 mg; Veramix, Up-john, ON, Canada). Ewes were examined for estrus with two vasectomized crayon-harnessed rams, and an electronic estrous detector for measuring changes in vaginal mucous impedance. The study began at the second estrus after the synchronization treatment.
The 14 ewes were in estrus within a 24-h period, and ovulated between 24 to 48 h after the onset of estrus. Days of ovulation were regarded as the days on which large (>5 mm in diameter) ovarian follicles that had been identified by ultrasonography were no longer detected. Nine days after estrus, or on about Day 8 after ovulation (7.7 ± 0.2 days; at 0800 h), seven ewes received a single injection of PGF2„ (15 mg i.m.; Lutalyse, Upjohn, Orangeville, ON, Canada) and an intravaginal MAP sponge, which remained in place for 6 days. Treatment with progestogen was designed to encapsulate the growth of follicles in the last two waves of the cycle.