The role of the uterus in ovarian control in the mare.

This research investigates how the removal of the uterus (hysterectomy) impacts the activity of ovaries in horses (mares). It was found that this procedure disrupts the normal secretion of progestins in the menstrual cycle, and causes irregularities in follicular activity and ovulation.

Study Background

• The study was designed to explore the effect of uterus removal on the functioning of ovaries in mares.
• Scholars pursued this investigation to understand the hormonal changes and disruptions manifested post-surgery.

Methods and Observations

• Four mares underwent hysterectomy, and their ovarian activities were studied.
• It was observed that the removal of the uterus interrupted the normal cyclic secretion pattern of progestins, which are major hormones in the reproductive cycle.
• Despite this interruption, all mares showed follicular activity, albeit with prolonged luteal activity.
• Notably, a significant number of follicles attained ovulatory size, even when ovulation did not occur.

Ovulation Patterns

• Ovulations were sporadic, observed in two of the four mares, despite variable progestin levels.
• All ovulations in the mares without a uterus were succeeded by the formation of Corpus Luteum (CL), a mass that develops in an ovary post-ovulation.
• However, the surge in progestins in the mares’ blood varied following CL formation – in some instances leading to significant increases, and in others, no change.

CL and Sexual Receptivity

• At the end of the experiment, the mares had CL with functional lifespans ranging between 48 to 77 days.
• The longest estimated CL lifespan in any hysterectomized mare was 137 days.
• It was also found that the ability of the ovary to convert pregnenolone to progesterone remained unaffected in the absence of a uterus.
• Sexual receptivity, typically associated with follicular growth and ovulation, didn’t occur in these hysterectomized mares in the presence of active CL.

Concluding Insights

• The research provides important insights into the role of the uterus in regulating ovarian functions in mares.
• The findings underscore the significant hormonal changes and irregularities in the reproductive functions following uterus removal, revealing potential implications for reproductive management in equines.