Efficacy of hCG and GnRH for inducing ovulation in the jenny

Knowledge about management of ovulation in the donkey is limited compared to that in the horse. This experiment was designed to evaluate the efficacy of injecting single doses of lecirelin (a GnRH-analogue) or of hCG to induce ovulation in the jenny and to determine whether effects are dependent upon follicular diameter at time of injection. Ovarian activity and follicular growth were monitored by rectal ultrasonography. Jennies were randomly allotted to the following groups: Group GnRH, treated with 100 μg lecirelin; Group hCG, treated with 2500 IU hCG; Group C, untreated and monitored for spontaneous ovulation. Animals were also categorized into subgroups depending upon follicular diameter: 30–35 mm (GnRH-1, hCG-1 and C-1) or 36–40 mm (GnRH-2, hCG-2 and C-2). Jennies in the two hormone treatment groups did not differ significantly for time from treatment to ovulation, but there was a significant reduction in time to ovulation as follicle size at treatment increased. Jennies treated with either lecirelin or hCG had significantly smaller follicle size at ovulation than jennies in the Control groups that underwent spontaneous ovulation. Treatment groups did not differ significantly in the proportion of jennies that ovulated within 48 h of injection or between 25 and 48 h following injection. These results highlight the usefulness of lecirelin for induction and synchronization of ovulation in the jenny, particularly since it would avoid the risk of reduced hCG response in reproductive management programs in which that hormone was repeatedly used.