Correlations between histologic endometrial lesions in mares and clinical response to intrauterine exposure with Streptococcus zooepidemicus.

The relationship between histologic lesions in endometrial biopsy specimens and susceptibility to chronic uterine infection (CUI) in mares was investigated. Mares were allotted to 4 groups on the basis of degree of endometrial lesions. Mares in group 1 (n = 6) had no pathologic changes, mares in group 2 (n = 5) had only mild pathologic changes, group-3 mares (n = 7) had moderate changes, and group-4 mares (n = 7) had severe inflammatory and fibrotic endometrial changes. Susceptibility to CUI was determined by the inflammatory response to intrauterine inoculation of 5 x 10(6) Streptococcus zooepidemicus. The inoculum was given on the third day of behavioral estrus and in the presence of a follicle > 30 mm. Mares with > 1 neutrophil/5 high-magnification (400 x) microscopic fields and > 20 colonies of S zooepidemicus at 96 hours after inoculation were considered to be susceptible to CUI. There was a significant association between biopsy grade and susceptibility to CUI among the groups. Histologically normal endometrium was associated with resistance to CUI, and severe histopathologic changes in the endometrium were associated with susceptibility to CUI. Mild to moderate endometrial lesions did not correlate consistently with susceptibility or resistance to CUI.