Induction of ovulation with buserelin in jennies: in search of the minimum effective dose

The aim of this study was to evaluate the minimum dose of buserelin acetate (buserelin) able to induce ovulation between 24 and 48 h from treatment (positive response) in estrous jennies. Jennies were studied during a total of 172 estrous cycles: ovarian activity was routinely monitored by ultrasound; when the dominant follicle reached a diameter of 33 ± 1 mm, estrous jennies were treated by subcutaneous administration of different doses of buserelin, 3.3mg (N = 11), 1.5mg (N = 21), 0.8 mg (N = 12), 0.4 mg (N = 16), 0.2mg (N = 13), 0.1mg (N = 16), 0.04 mg (N = 14), 0.02 mg (N = 16), or employed as controls (N = 53). Single jennies (P = 0.0001) and GnRH dose (P = 0.003) significantly affected ovulation rates. Ovulation rates between 24 and 48 h of each treated group, except for the 0.02 mg group, was higher than in the control group (P < 0.05). The minimum dose of buserelin effective to induce ovulation in estrous jennies was 0.04 mg.