Oxytocin administration prolongs luteal function in cyclic mares.

This research found that administering oxytocin to mares after ovulation can extend the functional state of the luteal phase, with the absence of luteolysis observed in the majority of the treated group.

Objective of the Study

The researchers sought to explore the role of the hormone oxytocin and its endometrial receptor in the ovulatory cycle of mares, focusing particularly on its potential influence on luteal function. They hypothesized that timely administration of oxytocin in cyclic mares might affect the pulsatile releases of prostaglandin F2 alpha from the endometrium, thereby influencing luteolysis – the degradation of the corpus luteum (the structure that forms on the ovary after an egg has been released).

Methodology

• The experiment involved administering oxytocin continuously to a group of five mares via subcutaneous minipump from days 8 to 20 after ovulation. This group was compared to a control group of four mares that were similarly infused with saline.
• In an additional experiment, oxytocin administration was delayed, beginning instead on day 10 post-ovulation.

Results

• The result of continuous oxytocin administration starting from day 8 after ovulation led to the inhibition of luteolysis in four out of the five treated mares, while the control group underwent the expected luteolysis.
• When oxytocin administration started on day 10 instead of day 8, luteolysis occurred rapidly in two out of the five treated mares. This effectively indicates a certain threshold period during which oxytocin responsiveness in these mares can become apparent, in this case, on or around day 10 of dioestrus.

Implications

From the results, it can be inferred that oxytocin administration has the potential to prolong luteal function in cyclic mares by inhibiting luteolysis. It also suggests that the timing of oxytocin administration might be key in determining its effects on a mare’s reproductive cycle. However, additional research is likely needed to fully understand the mechanisms behind these results and their potential implications in equine reproductive management.