Effects of GnRH and anti-PMSG injections on fertility in ewes pre-treated with MAP sponge and PMSG during the non-breeding season.

Abstract

Effects of synthetic gonadotropin releasing hormone (GnRH) and rabbit anti-pregnant mare serum gonadotropin (PMSG) on numbers of ovulation, fertility and prolificacy were investigated in 59 Suffolk ewes in which estrus was induced by a progestin (methyl-acetoxyprogesterone: MAP)-impregnated vaginal sponge and 750IU PMSG during anestrous season. The animals, at the time of estrus, were administered intramuscularly either with saline (group I), 150μg GnRH (group II), or rabbit anti-PMSG serum that could neutralize the potency of 750IU PMSG (group III) and artificially inseminated. A total of 56 ewes (group I: 18, group II: 19 and group III: 19) were inseminated with fresh-undiluted semen.. Although pregnancy rates were not significantly different among these groups, lambing rate in group II (57.9%) was significantly higher than group I (16.7%: P 5 mm in diameter, examined at the 8th day after PMSG treatment in 10 ewes per group, were also not significantly different among the groups. However, wastage proportion of eggs or embroys significantly (P<0.025) decreased in GnRH-injected ewes (64.3%) as compared with that in saline-treated ewes (90.0%). A decrease in the plasma concentration of estradiol-17β, caused by anti-PMSG treatment did not improve the fertility. These results indicate that a single intramuscular injection of GnRH at the onset of estrus, induced with MAP sponge and PMSG treatments, was effective for improvement of fertility in ewes during non-breeding season.