The influence of intrauterine saline infusion on luteal function and cyclical activity in the mare.

This research study investigates the effect of intrauterine saline infusion on the reproductive cycle in horses. It was found that saline infusion can induce early luteolysis, which is the degeneration of the corpus luteum in the ovary, resulting in a decrease in plasma progesterone levels and a shortened ovulation cycle.

Objective and Method

• The primary goal of this research was to understand the impact of an intrauterine saline infusion on the luteal function and cycle activity in mares. This was monitored by observing changes in the ovulatory interval and plasma progestagen levels post-infusion.
• The experiment was conducted on multiple dioestrous mares, a stage in the oestrous cycle where the mare is sexually inactive. The mares received the saline infusion at different stages post-ovulation, mainly Day 4 or 5, and Day 6 or 7.

Findings

• The study found that intrauterine saline infusion led to premature luteolysis or the degeneration of the corpus luteum. This, in turn, shortens the ovulatory interval or the period between two ovulations.
• The plasma progestagen levels began to decrease approximately one day post-infusion and had fallen to less than 1-0 ng/ml within four days. Progestagen, such as progesterone, is a hormone that prepares the uterus for pregnancy.

Additional Observations

• The researchers also observed that the corpus luteum (CL), including those formed from ovulations during dioestrus, must be at least 4 to 5 days old before saline infusion can induce luteolysis.
• Out of ten mares infused either on Day 4 or 5 post-ovulation, only six experienced a shortening in their ovulatory interval. Whereas, out of another ten mares infused on either Day 6 or 7 post-ovulation, seven experienced a shortening, and three failed to respond, mainly due to a coinciding dioestrous ovulation.
• In mares that responded to the treatment, the interval from saline infusion to the beginning of oestrus was found to be around 5 to 6 days; and from saline infusion to ovulation, it was approximately 9 to 10 days.