Susceptibility to Delayed Uterine Clearance After Breeding: Relationship to Endometrial Biopsy Score and Age, and Variations Between Seasons

The objectives of this study were to 1) compare delayed uterine clearance (DUC) after insemination with age and endometrial biopsy score (Kenney scale), and 2) compare susceptibility to DUC over subsequent breeding seasons. Fifty five mares were inseminated with 107 freeze-killed spermatozoa during estrus and evaluated for DUC by transrectal ultrasonography. Delayed uterine clearance was defined as >2 cm intrauterine fluid at 48 h and the presence of fluid at 96 h after insemination. Mares with no fluid retention 48 h after insemination were considered resistant to DUC, and mares with >2 cm of fluid at 48 h, but no fluid at 96 h were classified as “intermediate”. A subset of 14 mares was classified for susceptibility to DUC in two subsequent breeding seasons. Comparisons were made using a Chi-square test comparing biopsy score, fluid retention after insemination, and age. Significance was set at p < 0.05. [...]