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

This research looks into how the ovulation-inducing effect of human chorionic gonadotropin (hCG) in horses is influenced when dexamethasone is administered during breeding. It reveals that a single dose of dexamethasone does not interfere with the action of hCG.

Objective of the Study

• The study aims to understand the effect of dexamethasone, administered at the time of breeding, on the efficacy of hCG in inducing ovulation in mares. The focus of the study is on those horses that are prone to persistent mating-induced endometritis (PMIE), an inflammation of the inner lining of the uterus caused by repeated breeding.

Methods

• The study is based on a retrospective analysis of medical records from 152 mares over 223 cycles. The research takes into consideration 113 cycles in which the mares susceptible to PMIE were treated with hCG and a single dose of dexamethasone. These were then compared with 110 control cycles to understand the effect of dexamethasone on ovulation.
• The researchers checked for the occurrence of ovulation ultrasonographically, following the administration of the two drugs.

Results

• The study revealed that the use of dexamethasone did not stop or interfere with ovulation in mares that were at risk of PMIE. This indicates that hCG can effectively induce ovulation in these mares, even in the presence of dexamethasone when given as a single dose during breeding.

Conclusions

• The research concluded that while repeated doses of dexamethasone in early oestrus have previously been found to cause failure in ovulation, a single dose does not have such an effect.
• The findings established that a single dose of dexamethasone can be a useful modulator for PMIE in susceptible mares and it does not hinder the efficacy of hCG to prompt ovulation.