Sustained high progesterone concentrations during estradiol-progesterone based estrus synchronization protocol in Japanese Black cows affects fertility by influencing preovulatory follicle size and its ovulation

Abstract

Preovulatory follicle (POF) size during estrus synchronization has been reported as one of the factors affecting conception rate in cattle. In present study, to determine the effects of POF size on the fertility of Japanese Black cows, relationship between POF size and conception rates and the effects of progesterone (P4) concentration on POF size were examined. An intravaginal progesterone-releasing device (CIDR) insertion and estradiol benzoate (EB) injection were applied to cows (day 0). At CIDR removal (day 8), the cows were received prostaglandin F2α and subsequently artificially inseminated between days 10 and 11, after EB administration (day 9). The cow that did not ovulate within 3 days after insemination had a small POF (ranging 5 to 8 mm) at CIDR removal, and they did not get pregnant. Cows that ovulated within 3 days were classified based on the POF size as follows: 1) small follicles (SF): POF < 10 mm, 2) medium follicles (MF): 10 ≤ POF < 11 mm, and 3) large follicles (LF): POF ≥ 11 mm. There was no difference in conception rates between SF (78.0%), MF (73.5%) and LF (62.2%). Luteolysis during CIDR treatment occurred in all cows in MF and LF groups, however 39.1% in SF showed no luteolysis. In the cows with non-luteolysis in SF, POF size at CIDR removal was smaller than the luteolysis group in SF, MF and LF groups (P < 0.05). In Japanese Black cows, P4 concentrations during estrus synchronization affects fertility by controlling POF size and its ovulation rate