Leukocyte distribution in the equine endometrium as a response to acute induced endometritis

Endometritis is an important cause of fertility problems in the mare, and all mares develop endometritis following breeding but reproductively normal mares will clear the inflammation. The histological pattern during endometritis in the mare has been described qualitatively for diagnostic purposes, but the distribution of leukocytes has not previously been described. In this study, endometrial biopsies were collected from five mares during oestrus and dioestrus, and then 20 hours after inducing S. zooepidemicus endometritis in oestrus and dioestrus. Four mares were also bred to a stallion, providing biopsies from breeding-induced endometritis, 20 hours after breeding. Computerized image analysis was used to count inflammatory cells in the luminal epithelium, stratum compactum and stratum spongiosum of the endometrium. Lymphocyte numbers were higher in control samples during oestrus than during dioestrus, but were higher in streptococcal endometritis in oestrus and dioestrus than during breeding-induced endometritis. The same pattern applied to eosinophil numbers, whereas neutrophil numbers were lower during endometritis in dioestrus than during endometritis in oestrus.