Uterine clearance mechanisms during the early postovulatory period in mares.

The research investigates how the uterus of a mare (female horse) clears out foreign material during the early post-ovulatory period. Using different substances and bacteria, the study identified some uterine clearance mechanism dysfunction in mares susceptible to endometritis, an inflammation of the inner lining of the uterus.

Research Methodology

• To evaluate the uterine response, the researchers inoculated the uterus of 9 mares (4 resistant and 5 susceptible to endometritis) with Streptococcus zooepidemicus organisms, chromium-labeled (51Cr-labeled) microspheres of 15-microns size, and charcoal.
• The inoculation was performed at estrus (the period of sexual receptivity in female mammals) before ovulation during three different estrous cycles, namely 1, 3, and 5.
• Swab specimens were collected from the uterus and used for aerobic and anaerobic bacteriological cultures. Also, serum samples were collected for determining levels of progesterone hormone.

Results and Findings

• Streptococcus zooepidemicus was isolated from 67% of uterine specimens obtained from mares susceptible to endometritis, suggesting that these mares have a higher bacterial load in the uterus.
• Escherichia coli was found in two of ten uterine specimens that were subjected to aerobic incubation.
• No bacterial growth was recorded for anaerobic bacteriological cultures, suggesting that the bacterial contamination was strictly aerobic.
• Charcoal and chromium-labeled microspheres were found in some samples from susceptible mares, indicating these mares have slower uterine clearance rates.
• Mean fluid collected from mares susceptible to endometritis was significantly higher than from resistant ones, indicating the higher susceptibility of some mares to uterine infections.

Conclusion

• On the basis of the results, the research concluded that uterine cellular mechanisms and bactericidal mechanisms are dysfunctional during the early post-ovulatory period in mares susceptible to endometritis which explains their susceptibility.
• Despite the dysfunctionality, it appeared that the mechanisms responsible for the mechanical clearance of materials in the uterus remained undisturbed. This suggests that while there are some issues, the fundamental cleaning mechanisms still function properly.