Effects of progestagen, PMSG and artificial insemination time on fertility and prolificacy in Corriedale ewes

The aim of the present study was to evaluate the effect of two progestagens, two doses of pregnant mare serum gonadotropin (PMSG) and two different instances of Al on fertility and prolificacy in Corriedale ewes during the breeding season. For the experiment, 120 ewes were divided at random into an experimental design of 2 x 2 x 2 factorial with 15 females in each group. The two progestagens were medroxyprogesterone acetate (MAP, 60 mg) or fluorgestone acetate (FGA, 30 mg), administered via intravaginal sponges. PMSG at a dose of 250IU or sterile saline solution was used and two periods when artificial insemination was carried out, 48 or 60 h after sponge removal. Each ewe was inseminated in the external os of the first cervical fold with one dose of refrigerated semen containing 500 million spermatozoa in straws. The fertility rates for MAP, FGA, PMSG, saline, and AI at 48 h and 60 h were 56.6%, 56.1%, 57.7%, 55.2%, 50.9% and 61.8%, respectively. The prolificacy rates for the same groups were 110%, 122%, 120%, 113%, 114% and 118%, respectively. Insemination at 60 h seemed to improve the fertility (P < 0.05), The interactions progestagen x PMSG, progestagen x time, PMSG x time and progestagen x PMSG x time did not show differences in fertility and prolificacy among groups (P > 0.05).