The effects of dexamethasone and prednisolone on pituitary and ovarian function in the mare.

The researchers in this article aimed to assess the impacts of the prolonged use of glucocorticoids, specifically dexamethasone and prednisolone, on a mare’s pituitary and ovarian functions. They found that using dexamethasone results in decreased uterine swelling, LH suppression, and a high ovulation failure rate, indicating possible adverse effects on a mare’s reproductive function when used for treating endometritis induced by ongoing mating.

Research Methodology

• Eighteen cycling Quarter Horse mares in their early oestrus stages were selected and divided randomly into three groups. Each group was subjected to different treatments for five days, which were dexamethasone, prednisolone, and a placebo.
• The dexamethasone group was given a dosage of 0.05 mg/kg body weight intravenously twice a day. The prednisolone group was orally administered a dosage of 0.5 mg/kg twice a day.
• Throughout the course of treatment, the mares were regularly evaluated through ultrasound scans to track their reproductive function. Blood samples were also taken daily to measure the levels of luteinising hormone (LH), progesterone, and cortisol in their bodies.

Findings

• The study found that dexamethasone treatment significantly reduced the concentration of endogenous cortisol compared to prednisolone or placebo treatments.
• After 24 hours of treatment, mares who were treated with dexamethasone showed decreased uterine edema scores compared to the other two groups.
• The rate of ovulation was observed to be significantly lower (40%) in the dexamethasone group compared to the prednisolone (83%) and placebo groups (100%).
• A lack of a LH surge was reported in three out of five mares in the dexamethasone group and one out of six mares in the prednisolone group.

Conclusion

• The study concludes that prolonged use of dexamethasone in mares during oestrus leads to decreased uterine oedema, impeded LH surge, and a high rate of ovulation failure. Thus, suggesting dexamethasone can have a negative impact on the mare’s reproductive health.
• Based on these findings, the researchers recommended limiting dexamethasone administration to just one or two days and considering reducing the dosage when managing persistent mating induced endometritis. This is to avoid any potential adverse effects on the mare’s reproductive function.