Efficacy of human chorionic gonadotropin to induce ovulation in the mare, when associated with a single dose of dexamethasone administered at breeding time

Abstract

Human chorionic gonadotropin (hCG) and dexamethasone have a role in the reproductive management protocols of mares susceptible to persistent mating-induced endometritis (PMIE). However, it is possible that there is interference between these 2 drugs. The objective of this retrospective study was to determine the efficacy of hCG to induce ovulation in mares treated with dexamethasone at breeding time. Medical records from 152 mares and 223 cycles were analysed. In 113 cycles, mares susceptible to PMIE were treated with 1500 iu hCG and a single dose of 50 mg dexamethasone, 110 cycles were used as controls and subsequent ovulation was assessed ultrasonographically and compared. Dexamethasone did not inhibit ovulation in mares susceptible to PMIE. Multiple administrations of dexamethasone to mares in early oestrus have induced ovulation failure. However, a single dose of dexamethasone, administered at breeding time, has been used as an effective modulator of PMIE in susceptible mares and does not interfere with efficacy of hCG to induce ovulation.