Placentitis is a common cause of late term abortion in mares. Based on morphologic lesions and pathogenesis, four different types of placentitis have been identified: (1) ascending placentitis (2) focal mucoid placentitis (3) diffuse placentitis and (4) multifocal placentitis. In most cases, infection of the placenta results in subsequent infection of the fetus and the release of prostaglandins from the inflamed placenta, which ultimately leads to abortion or delivery of a premature foal.
... emature foal. Affected foals may experience accelerated fetal maturation in response to the inflammatory environment. They are typically delivered prematurely, but are often mature enough to survive in the extrauterine environment. It has been suggested that indirect stimulation of the fetal hypothalamic-pituitary-adrenal axis by pro-inflammatory cytokines is responsible for precocious fetal maturation and that delaying premature labor long enough to allow accelerated fetal maturation to occur may improve foal survival rates. To achieve this goal, it is necessary to promptly diagnose and effectively treat the disease before clinical signs are observed. No single sample test appears to have sufficient specificity and sensitivity to accurately detect subclinical cases of placentitis. Therefore the development of a panel of diagnostic tests that accurately indicate inflammation as well as placental insult is needed. Transrectal and transabdominal ultrasound, combined with endocrinological (progesterone, estrogen and relaxin), and inflammatory biomarkers such as acute phase protein assays, may provide additional tools for diagnosing subclinical placentitis and monitoring progression of the disease in mares. These tests could be used to regularly monitor placental health during late pregnancy, and allow us to treat the condition at an early stage. Treatment strategies for mares with ascending placentitis are directed at several factors including combating infection (antibiotics), reducing inflammation (NSAIDs) and controlling myometrial activity (progestins). Although selected antibiotics cross the placenta, fetal fluid concentrations are consistently significantly lower than in serum, often resulting in a suppression rather than elimination of bacterial growth in the placenta and the allantoic fluid. It should therefore, be of high priority to identify antibiotics that can be administered in doses that cross the placenta and maintain sufficient concentrations for a sustained duration of time. A recent study suggests that when mares with placentitis are treated successfully, the future athletic performance of their foals does not appear to be affected.