Litter size affects ovulation and pregnancy rate after a hormonal treatment without influencing expression of estrus in the anestrous season in ewes

Abstract

The aim of this study was to determine if litter size affects the response to hormonal treatments for inducing estrus and ovulation during the non-breeding season. A total of 124 Corriedale ewes were utilized, consisting of 56 ewes that had given birth during the spring and were currently nursing either a single lamb (Single, n = 30) or twin lambs (Twin, n = 26). Additionally, a control group of ewes that had not given birth (Con, n = 68) was included. Estrus was induced 38 days after lambing using intravaginal sponges containing medroxyprogesterone acetate, which were left in place for 7 days. Furthermore, 350 IU of eCG was administered at the time of sponge removal. Upon detection of estrus, the ewes were inseminated, and transrectal ultrasonography was performed 8 and 40 days later to determine the presence of a corpus luteum (CL) and pregnancy, respectively. Expression of estrus did not differ due to postpartum status. However, a higher proportion of Con ewes than Twin ewes had a corpus luteum (P = 0.02), while the Single group did not differ from the other groups. Conception and pregnancy rates were higher in the Con group than in both, the Single and Twin groups (P ≤ 0.03). The litter size did not have a significant effect on the estrous response; however, postpartum status and/or lactation negatively impacted the pregnancy outcome.