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Pferdeheilkunde 24 56 IntroductionIn the past, endometritis was believed to exclusively be the result of bacterial contamination of the uterus (Asbury and Lyle 1993). Treatment strategies were focused on preventing bacteria from entering the uterus, and/or administration of antibiotics. Hughes and Loy (1969) demonstrated that young reproductively sound mares had natural resistance to an experimentally induced infection. They concluded that local components of uterine defense were responsible for the effective and rapid clearance of bacteria in mares with natural resistance to uterine infection. Mares that failed to spontaneously clear the uterus from bacteria were classified as susceptible to persistent endometritis. Subsequent research on uterine defense mechanisms has increased our understanding of the pathophysiology of equine endometritis. Causative agents have been identified, and we have learned to distinguish between uterine infection and a physiological breeding-induced endometritis resulting from uterine exposure to semen (Troedsson et al. 1995a, Troedsson 1999. Additionally, more effective management and treatment protocols have reduced the effect of endometritis on fertility. However, endometritis remains a major clinical problem in brood mare practice. The reasons for this may be that effective management/treatment of "susceptible" mares have resulted in maintaining these mares within our brood mare population, possibly also affecting the gene pool. Breeding-induced endometritisIntrauterine deposition of equine semen causes an inflammatory reaction resulting from spermatozoa (Kotilainen et al. SummaryBreeding-induced endometritis is a physiological reaction to semen. It is an important part of normal sperm transport to the oviduct as well as elimination of excess sperm from the uterus. In 10-15% of brood mares, the normal clearance mechanism fails resulting in a persistent breeding-induced endometritis with severe consequences on fertility. The cause of persistent breeding-induce endometritis is believed to be impaired myometrial activity in response to uterine inflammation. However, disruption of normal breeding activities may also contribute to the condition. Social interaction with a stallion appears to be important to normal uterine contractility after breeding. The presence of seminal plasma in an inseminate has also been shown to be of importance to normal sperm transport and elimination from the female tract, as well as in the modulation of the breeding-induced inflammation. Treatment of persistent breeding-induced endometritis has been focused on assisting the uterus to clear the inflammation in a timely fashion. Post-breeding treatments with oxytocin or prostaglandins and/or uterine lavage at 6-24 hours after breeding have been used by practitioners with good success. Alternative treatments such as the use of corticosteroids, immunostimulants, and acupuncture have recently been suggested to improve uterine clearance and fertility in mares that are susceptible to persistent breeding-induced ...

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