A single subcutaneous administration of buserelin induces ovulation in the mare: field data

The aim of the present study, was to evaluate whether a single subcutaneous administration of the GnRH analogue buserelin could induce ovulation in the mare during the breeding season. Two studies were carried out under field conditions. In Experiment 1, 90 cycles of trotter mares aged 2-7 years, were assigned to a buserelin group (Bus1) or to a control group (Control), in the presence of a >/=35 mm pre-ovulatory follicle, with uterine oedema and a relaxed cervix. Ten mares were assigned to the two groups for 32 cycles in Bus1 and 52 cycles in Control, two mares received only Bus1 for three cycles, and one mare was assigned to Control for three cycles. Mares treated with buserelin received 6 ml of SUPREFACT s.c. (1.05 mg/ml buserelin acetate), and no treatment was given in Control. The ovulation rate between 24 and 48 h was higher (p < 0.0001) in Bus1 (31/35) than in Control (15/55). In Experiment 2, the condition of inducing ovulation with 6 ml SUPREFACT s.c. (Bus2) or 1500 ui human chorionic gonadotropin were identical to the first study. Forty-nine mares of ages 2-21 years, were used for 120 cycles, 56 cycles were assigned to Bus2, and 64 cycles were induced with 1500 IU human chorionic gonadotropin i.v. No significant difference was found in the ovulation rate on day 2 (38/56, 50/64), or in the fertility rate (19/48, 26/57). No negative effect of the treatment was observed with repeated buserelin administration in either study during the breeding season. We can conclude that a single administration of buserelin induces ovulation in the mare, under suitable conditions for veterinary practitioners.