Induction of Early Cyclicity Using Estradiol Cypionate and Sulpiride on Seasonally Anestrous Mares

Abstract

This study was designed to evaluate strategies to induce early ovulation in anestrous mares. Thirty-two seasonally anovulatory mares were randomly placed into 4 treatment groups based on their reproductive status. Anestrous (n = 11), transitional (n = 8), and progesterone pre-treated (n = 9) groups were treated in January with 50 mg of estradiol cypionate (ECP) followed 24 h later with 3 g of sulpiride. A control group (C, n = 4) was administered the treatment carrier. Ovaries were scanned every 2 to 3 d via transrectal ultrasound for 60 d following treatment. Day of first and second ovulation was recorded. Embryos were transferred to 10 mares after at least 2 estrous cycles. Blood samples were analyzed for luteinizing hormone (LH) and prolactin (PRL). There was an effect of treatment (P < 0.001) on mean number of days to first ovulation. Mean number of days to first ovulation was less (P < 0.001) in all treated groups than C. There was an effect of treatment on the number of mares that achieved first ovulation (P < 0.001) and second ovulation (P = 0.018). Of 28 treated mares, 23 (82.1%) ovulated within 22 d of treatment. Of 23 mares that had a first ovulation, 15 (65.2%) had a second ovulation within 43 d. There was an effect of the treatment-by-day interaction on plasma mean PRL (P < 0.001) and LH (P = 0.021) concentrations. Ten embryos were transferred across the 3 ECP-sulpiride treated groups with 70% of mares having confirmed pregnancy at 60 d.