A major cause of abortions and the birth of premature foals is ascending placentitis.  Clinical signs noted in most but not all mares with ascending placentitis are a vaginal discharge and premature udder swelling.  Ascending placentitis occurs when an infectious agent enters a pregnant mare’s cervix and subsequently infects the placenta or fetal membranes.  The result of this infection is usually fetal stress that leads to abortion or premature delivery.

Our ability to evaluate fetal viability is only fair.  Dr. Michelle Leblanc from Lexington, Kentucky, reports many hormones have been evaluated to determine if any reliably measure fetal viability.  Her research revealed that single hormonal samples are not very helpful in evaluating the fetus.  However, the measurement of multiple progesterone samples can be useful as mares subjected to experimental placentitis either had a premature rise or rapid decline in progesterone level.
 
Trans- abdominal ultrasound exam of the uterus and placenta can be used to identify a compromised fetus.  Ultrasound exam can determine placental thickening or separation of the uterus and placenta.  In a recent study of experimental placentitis, 80% of the mares with placentitis exhibited placental thickening or placental separation before they aborted or delivered a premature foal.  If a mare aborts or delivers a premature foal, a uterine culture should be performed to determine the causative organism.  Also, the aborted fetus should be examined by a veterinarian as the causative organism can also usually be cultured from the foal’s stomach contents. 

If a diagnosis of placentitis is made in time, antibiotic and hormonal therapy can sometimes be successful.  If your pregnant mare develops a vaginal discharge or bags up prematurely, call your vet.