Microscopic examination of endometrial biopsies of retired sports mares: an explanation for the clinically observed subfertility?

The research investigates why retired sport mares (female horses) often experience reduced fertility. These findings reveal that most suffer from alterations in the lining of the uterus, or endometrium, and that these alterations might be a significant factor contributing to subfertility.

Objective of the Study

• The main goal of this research was to ascertain possible reasons for the observed subfertility in retired sports mares.
• To achieve this, the researchers conducted microscopic evaluations on endometrial biopsies collected from 189 retired sports mares.

Findings of the Study

• The mares studied, aged between 3 and 23 years, displayed signs of endometritis (30%) and endometrosis (77%), both being conditions that involve inflammation of the endometrium. Mild forms of these conditions were more common.
• When examining the mares biopsied during the breeding season, 50% showed disorders in glandular differentiation. This includes glandular inactivity (8%) and irregular glandular differentiation (42%).
• Contrasting these results with existing literature, retired sports mares have a higher prevalence of glandular differentiation disorders compared to primarily non-performance mares. The frequencies of endometrosis and endometritis were similar in both groups.
• It was noted that the most common cause of glandular differentiation disorders is ovarian dysfunction.

Implication of the Findings

• The results suggest a potential link between the glandular maldifferentiation of the endometrium and the observed low fertility in retired sports mares.
• The underlying cause of this abnormal glandular differentiation, ovarian dysfunction, can also be a crucial area of study in understanding and addressing this issue of subfertility in retired performance mares.