What Are the Options for Induction of Ovulation in the Mare in Europe? Buserelin as an Alternative to Human Chorionic Gonadotropin

A pharmaceutical survey conducted among veterinary surgeons practising in Europe (n = 46) revealed that the first choice drug to induce ovulation in the mare is human chorionic gonadotropin (hCG) (91%) and the second choice was a deslorelin implant (Ovuplant; 64.7%). The reason for not using the second choice drug more often was because, although more effective, it was more expensive (66.7%) or more difficult to obtain (20% of responses). In a parallel retrospective study, the efficacy of four different dose rates of buserelin acetate (Suprefact, 1 mg/mL, Sanofi-Aventis; 1 mg, 0.5 mg, 0.25 mg, and 0.125 mg) to induce timely ovulation (within 48 hours of treatment) was compared in 94 mares examined for the occurrence of ovulation three times a day during 225 estrous cycles in 1 year. The ovulatory responses in mares (84.8%, 87.9%, 88.5, and 90%) were similar (P > .05) for all four buserelin doses, 0.125, 0.25, 0.5, and 1 mg, respectively. Transitional mares failed to respond more frequently (34.5% follicles regressed) and took longer to ovulate (36.8% of cycles had an interval to ovulation >48 hours) than cyclic mares (0.0% of follicles regressed and 8.9% of intervals to ovulation >48 hours) following treatment of 0.5 mg of buserelin (P < .05). Furthermore, 21 mares (median age 15.5 years old) were treated with 1,500 IU of hCG in 54 cycles and with buserelin in 137 cycles. The ovulatory response to hCG (25.6%) was lower (P < .05) in these mares than that to buserelin (85.8%).