The effect of various doses of hCG on induction of ovulation in mares

Abstract

In this study, the influence of various doses of hCG on induction of ovulation in cycling mares is investigated. A total of 38 thoroughbred mares having a ? 35 mm follicle were treated intramuscularly with 4500 IU hCG (Group A, n=12), 3000 IU hCG (Group B, n=12) or 2 ml physiological saline (Group C, n=14, control). The average injection-ovulation interval (hr) was significantly shorter (P < 0.05) both hCG treated groups when compared to control group. The differences of estais duration (hr) among the groups were not significant. The percentage of ovulation within 48 hours after treatment significantly (P < 0.05) increased in mares treated both 4500 IU hCG (83.3%) and 3000 IU hCG (75.0%) when compared to control animals (21.4%). However, there was no significant difference in the percentage of ovulation within 48 h between hCG treated mares. In conclusion, administration of 3000 IU hCG is sufficient for induction of ovulation within 48h in mares which had a dominant follicle of ? 35 mm.