Factors Affecting the Ovarian Response to a Combined Estradiol-Sulpiride Treatment in Seasonally Anovulatory Mares

© 2016 Elsevier Inc. Twenty-three seasonally anovulatory mares, housed at two separate farms, were treated with 50 mg of estradiol cypionate (ECP) and 3 g of sulpiride in January to study factors that contributed to success of the treatment (response = ovulation within 28 days). Every other day, blood samples and pretreatment secretagogue challenges were used to characterize prolactin, luteinizing hormone (LH), insulin-like growth factor-I, leptin, and insulin concentrations. Ovaries of each mare were scanned via ultrasound regularly until detection of a 32–35 mm follicle, at which time the mare was artificially inseminated. Prolactin was stimulated in all treated mares and was similar (P \u3e .05) in responding and nonresponding mares. Nine mares, all at the same farm (Ben Hur; farm effect, P = .006), responded with preovulatory sized follicles within 20 days of treatment. Five of the 9 were inseminated and 3 conceived. Retrospective analysis revealed that of the mares responding, body condition score (P = .03), body weight (P = .02), plasma concentrations of insulin (P = .01) and leptin (P = .09), and pretreatment response of LH to gonadotropin-releasing hormone (P = .106) were higher in responding than in nonresponding mares. In general, factors that differed and may contribute to whether a given mare responds to this ECP-sulpiride protocol were mainly characteristics pointing toward well-nourished mares. Minor nutritional differences between farms likely played a role in the lack of success on the one farm. Also, the LH response to gonadotropin-releasing hormone prior to treatment may be indicative of the subsequent LH response to ECP-sulpiride and hence the ovarian response