The effect of exogenous oxytocin on luteal function in mares.

The research investigated the impact of externally administered oxytocin on the menstrual cycle of horses and found that the hormone did not alter the luteal phase or induce luteolysis–the degradation of the corpus luteum.

Research Purpose and Methodology

• The aim of this study was to explore the effect of oxytocin, a hormone commonly associated with labor and breastfeeding in humans, on the luteal function in mares (female horses).
• Luteal function refers to the activities of the corpus luteum, a structure that develops in the ovary after ovulation and produces progesterone, a hormone vital for maintaining pregnancy.
• Luteolysis signifies the natural degeneration of the corpus luteum towards the end of the menstrual cycle if there’s no pregnancy.
• The researchers administered daily injections of 150 units of oxytocin to six mares on Days 4 to 8 after ovulation. In addition, three mares received estrogen injections 24 hours before an oxytocin injection on Day 7.

Results

• The oxytocin injections did not induce luteolysis, as indicated by the mares maintaining normal plasma progestagen concentrations. Progestagens are synthetically produced steroids that mimic progesterone.
• Despite the oxytocin and estrogen treatments, the ovulatory intervals (the period from one ovulation to the next) in most subjects remained normal, suggesting the hormonal interventions did not affect their menstrual cycles.
• On the contrary, an unusual corpus luteum that persisted for 46 days developed in one mare. However, the reasons behind this anomaly, and its potential links to the hormone treatments, were not explored in the study.

Conclusion

• The study concluded that external oxytocin does not induce luteolysis in mares, at least not in the dosages and administration schedule used in this research. Therefore, it appears that administering oxytocin does not significantly impact the luteal phase of the mares’ ovulation cycle.