Induction of Short Ovulatory Cycle in Shiba-Goats by Repeated Treatments with Prostaglandin F2.ALPHA..

Abstract

Follicular growth of ruminant species occurs more than once during an estrous cycle either resulting in ovulation (ovulatory follicular wave) or not resulting in ovulation (latent follicular wave). Using Shiba-goats, we examined if ovulation could be induced from every latent follicular wave and if the resulting ova were fertile. Ovarian follicular development was monitored daily by transrectal ultrasonographic examination in 20 female goats for 2 consecutive estrous cycles. After the second spontaneous ovulation (day 0 = ovulation), all animals were each treated with a luteolytic dose of prostaglandin F2α (PGF 2α) on days 3 and 4,which resulted in ovulation from the first latent wave. Fertile males goats (n=2) were immediately introduced to the first group of animals (n=5), resulting in 4 pregnancies. For the second group of goats (n=9), 4 consecutive short estrous cycles were induced by the PGF2 α treatment at a mean interval of 6.5 ± 1.2 days with a range of 4-9 days. Five of 9 goats were allowed to mate following 4 consecutive short ovulatory cycles; normal behavioral estrus was observed at each estrus, and four of five animals became pregnant. The third group of goats (n=6), in addition to PGF2α treatment, received exogenous progesterone supplement which allowed latent follicular development to occur, but prevented ovulation until the effect of progesterone supplement subsided. These results suggest that female Shiba-goats possess physiological mechanisms for the final steps of follicular maturation and subsequent ovulation at short intervals when progesterone production from the newly developed corpus luteum is terminated.