Placentitis in Mares

Placentitis, a fungal or bacterial infection of the placenta, often shows no signs until the condition is so far advanced that the mare goes into premature labor and delivers a dead or extremely sick, weak foal. A study conducted in Australia found that in a recent Thoroughbred breeding season, more than 1,700 foals were lost due to placentitis, making this problem a significant one.

Researchers looked at the treatment, ultrasound findings, mare’s age, breeding history, fetal activity, condition of the placenta, and condition of neonatal foals from 159 mares that had premature births in the third trimester of pregnancy. Severity of the infection and treatment after diagnosis were found to be most important in a foal’s condition at birth and its and ultimate survival. Mares presenting with vaginal discharge usually had poorer outcomes.

Treatment with potentiated sulphonamide antibiotic led to a more positive outcome. In this study, factors that had no bearing on outcome included mare’s age, number of previous pregnancies, presence of premature lactation, and choice of treatment with NSAIDs or altrenogest.

The researchers recommended that veterinarians should use both transrectal and transabdominal ultrasound scanning to assess mares that show signs of premature labor. Using more than one scan gives a better chance to evaluate separation of the placenta close to the cervical pole, fetal heart rate, and folding of the placenta in the pregnant horn of the uterus.