Antibacterial activity of mare uterine fluid

Luminal fluid from the mare uterus was used to investigate its relation to antibacterial defenses. Uterine flushings were collected at Day 3 of estrus, Day 8 postovulation and Day 15 postovulation. Uterine proteins were concentrated by ultrafiltration, dialyzed and examined for chemotactic activity to neutrophils and for antibacterial properties. Serum taken at the time of flushing was dialyzed and studied in a similar manner. Neutrophil migration in response to serum from Day 3 estrus and Day 8 postovulation was increased (P less than 0.05) above controls. Uterine protein from Day 8 postovulation and from Day 3 of estrus also stimulated neutrophil migration (P less than 0.05) above values of controls. Antibacterial activity was measured by incubation of S. zooepidemicus with concentrated uterine flushing or serum. Serum from all three estrous cycle intervals diluted 1:10 or used at a protein concentration equal to the protein concentration of uterine fluid did not inhibit growth. After 4 h of incubation, bacterial growth in estrous serum was significantly greater (P less than 0.01) than serum taken at Day 8 and Day 15 postovulation. Uterine flushings from Day 8 postovulation significantly decreased bacterial colony-forming units (P less than 0.01). Heating flushings at 56 degrees C for 30 min did not abolish the antimicrobial activity, while heating flushings for 30 min at 80 degrees C removed this activity. The antibacterial activity does not appear to be due to agglutinating antibody.