Endometrial histology and post-partum mares treated with progesterone and synthetic GnRH (AY-24,031).

This research article explores how treatment with progesterone and synthetic Gonadotropin Releasing Hormone (GnRH) affects uterine tissue and ovulation timing in post-partum mares.

Background and Approach

• The purpose of this study was to examine how certain hormones affect the reproductive cycle in horses after giving birth.
• The study focused on the foal heat, which is the first estrus or fertile period experienced by a mare after the birth of a foal.
• Progesterone was used due to its role in pregnancy and reproduction, while synthetic GnRH was used due to its role in regulating the secretion of hormones that stimulate the ovaries.
• The treatment involved applying 200 mg of progesterone from Days 5-14 post-partum, while nine mares received 2 mg of GnRH from Day 2 of the progesterone-delayed estrus.

Findings

• Initially, they found that administering progesterone in oil significantly delayed the onset of foal heat.
• Using the treatment did not significantly shorten estrus or hasten ovulation when combined with synthetic GnRH, dispelling any hypotheses the researchers may have had about the efficacy of this method.
• The research team took uterine biopsies on Day 15 post-partum and found a mixed endometrial morphology, with characteristics of both estrus and diestrus.
• Interestingly, they saw an increased proliferation of endometrial gland cells during ovulation, compared to control mares experiencing a normal foal heat.

Significance

• This research holds potential implications for equine reproductive management.
• The findings that progesterone delays foal heat but does not hasten ovulation or shorten estrus could lead to changes in how hormones are used to manage breeding.
• While the results did not indicate a significant hastening of ovulation, the mixed endometrial morphology could warrant more investigation.
• The increased gland proliferation seen in treated mares suggests that hormonal treatments might have far-reaching implications for the health and fertility of mares.