Early pregnancy loss in a mare due to possible acute uterine bacterial infection

This case involves an 11-year Haflinger mare with breeding induced endometritis. After breeding soundness examination, mare was inseminated twice during 1 estrous cycle. On day 1 (day 0 = day of ovulation), mare was negative for endometrial cytology and culture. On day 10, an embryonic vesicle was visualized via transrectal ultrasonography; progesterone concentrations were 15.8 ng/ml. On day 11, the embryonic vesicle had increased to a diameter of 0.8 cm with clearly visible endometrial edema; progesterone concentrations were 14.4 ng/ml. On day 12, embryonic vesicle was no longer visible; progesterone concentrations were 4.7 ng/ml (possibility of premature luteolysis). Bacteriological culture of the uterus with a guarded endometrial swab had a pure culture of Streptococcus equi subspecies zooepidemicus (S. zooepidemicus). Mare underwent treatment (uterine lavage and systemic penicillin for 5 days) and became pregnant at the next estrus. This case highlighted the possibility of S. zooepidemicus subclinical endometrial infection, not diagnosed by routine endometrial cytology and culture, becoming dormant.