Factors affecting uterine clearance of inoculated materials in mares.

This research article discusses an experiment investigating how age and reproductive status affect the speed at which mares’ uteruses clear materials that were artificially introduced. The findings suggest that younger mares clear the materials more rapidly, potentially making them more resistant to bacterial infections.

Experiment Overview

• The researchers conducted their experiment on twelve acyclic mares, who varied in both age, ranging from 2 – 29 years old, and parity, meaning reproductive status, which varied from maiden to multiparous (having given birth multiple times).
• The mares were treated with the hormones oestradiol-17 beta or progesterone to induce conditions in the endometrium similar to those during estrus (oestradiol-17 beta treatment) and diestrus (progesterone treatment). These hormonal changes mimic the typical reproductive cycle.

Procedure of Inoculation

• Once the hormone treatment was administered, the mares’ uteruses were artificially filled (inoculated) with 50 milliliters of saline solution which contained one or more of the following: Streptococcus zooepidemicus bacteria, 51Cr-labelled 15-micron microspheres, and 500 mg of charcoal.
• Five hours after the inoculation, the uteri were flushed with another saline solution, which included trace amounts of 125I-labelled HSA.

Results and Analysis

• In the group of mares treated with oestradiol-17 beta (Group E + B), younger horses cleared the inoculated materials more quickly than older ones. There also appeared to be a significant positive correlation between the mares’ age and the concentration of bacteria, the total number of bacteria, and quantity of microspheres and charcoal remaining in the uterus. Also, there was a correlation between age and white blood cell (WBC) concentration and total number of WBCs.
• In the group that received only microspheres and charcoal (Group EC), results showed a similar pattern. Age seemed to be positively correlated with the amount of microspheres and charcoal not cleared, as well as with WBC concentration and total number of WBCs.
• This research suggests that in uteruses dominated by estrogen, physical drainage speed may play a role in determining whether a mare is more ‘resistant’ or ‘susceptible’ to bacterial infections. This physical clearance seemed to be faster in younger mares (i.e., the ‘resistant’ ones), whether or not there was an antigenic stimulus.
• In the progesterone-treated mares (Group P + B), there were no clear correlations between age and the materials’ clearance speed and amount.