The mare’s reproductive tract is similar to the respiratory tract in that both have mucosal immune systems. In both areas, the mucosal immune system is capable of producing excessive quantities of mucus when persistently irritated. Robert C. Causey, DVM, PhD, an associate professor in Animal and Veterinary Sciences at the University of Maine, discussed the pathologic effects of clinical uterine inflammation on the equine endometrial mucosa at the 2008 American Association of Equine Practitioners Convention, held Dec. 6-10 in San Diego, Calif.

Excessive mucus can interfere with penetration of uterine antibiotics, sperm motility, and migration of an embryo before it becomes fixed in the uterus for further development. These disruptions can result in subfertility. Causey said previous studies indicated that mucus secretion increases during experimental uterine inflammation and also increases in mares with delayed uterine clearance (of contaminants after breeding).

To determine what was occurring in mares with endrometritis (infection of the uterine lining) compared with healthy mares, Causey and colleagues conducted a study of 34 mares. Of that number 10 were listed as being reproductively normal and 24 were listed as having been diagnosed with endometritis. Uterine biopsies were taken of all mares involved in the study.

The results revealed that persistent inflammation did stimulate disruption of the lining of the uterus and excessive mucus production. Veterinarians might recommend mucolytic agents (which dissolve mucus), steroids, or prolonged sexual rest for the mare to restore endometrial function.