Regulation of follicular activity and ovulation in ewes by exogenous progestagen

Abstract The success of estrus synchronization programs using progestagen sponges, particularly for fixed-time Al, varies considerably. In view of the recent evidence in cattle that exogenous progestins alter follicular dynamics, it may be that the stage of the estrous cycle at which the synchronization protocol is begun. affects the synchrony of ovulation. The goal of this study was to evaluate the effect of medroxyprogesterone acetate (MAP) intravaginal sponges on follicular dynamics, luteal function and interval to ovulation when inserted at 3 stages of the estrous cycle. Sponges were inserted for 12 d beginning on either Day 0, 6 or 12 (n=5) following ovulation. Ovarian activity was monitored using real-time ultrasound imaging during the treatment and the post-treatment estrous cycles. Information from the post-treatment cycle was used as a baseline to compare with the treatment cycle. Most ewes (79%) in the post-treatment cycle exhibited 3 follicular waves in an estrous cycle of 16 d, with the second wave follicles having smaller diameter (P 0.01) in waves in the early and middle of the 12-d MAP treatment period when compared with the last 4 days. This effect was most pronounced when endogenous progesterone concentrations were elevated concurrently with the presence of the sponge. Persistence of the ovulatory follicle was increased (P