Ultrastructural and histological characteristics of the equine endometrium at day 5 post ovulation.

This research aimed to investigate the microscopic changes in the uterine wall of horses at day 5 after ovulation, comparing those changes in horses that were inseminated and those left to naturally cycle. The findings suggest that significant changes occur in inseminated horses, possibly preparing the uterus for pregnancy or indicating inflammation due to the insemination process.

Objective

The main goal of this study was to observe and document the microscopic (ultrastructural and histological) changes of the uterine endometrium at day 5 after ovulation in both inseminated and naturally cycling (not inseminated) mares.

Methodology

• The study included mares which were examined daily through transrectal palpation and ultrasonographic examination of the reproductive tract to detect ovulation.
• In their first cycle, endometrial biopsies were taken on day 5 post-ovulation from 10 mares which weren’t inseminated, forming the “Cyclic group”.
• In the next cycle, the same mares were inseminated with fresh semen from a fertile stallion, and further endometrial biopsies were taken on day 5, creating the “Inseminated group”.
• The Inseminated group was further divided into two subgroups based on the exact timing of the biopsy, either day 5-5.5 or day 5.5-6.
• The biopsy samples were then analyzed through scanning electron microscopy and light microscopy to observe the changes at the microscopic level.

Results

• The inseminated group showed an increase in glandular diameter and lymphocyte population, and a decrease in ciliated cell population compared to the cyclic (non-inseminated) group.
• However, the study found no differences between the cyclic and inseminated groups in terms of several variables, such as number of micro-ciliated polygonal cells, amount of secretion over the epithelium, glandular density, and others.
• Moreover, no significant differences were observed between the two subgroups of the inseminated group based on the exact moment of biopsy collection.

Conclusions

• The study concluded that there were significant ultrastructural and histological changes in the endometrium on day 5 post ovulation in inseminated mares.
• The authors suggest two potential hypotheses for these changes: either signaling mechanisms are preparing the uterus for an impending pregnancy, or these changes are inflammatory responses due to the residual effects of semen post-insemination.