Losing a foal any time during gestation is heartbreaking for breeders, but even more so when it happens near term. What can owners and veterinarians do to prevent late-term abortion, especially those that result from infections in the placenta?

"Minimizing late-term abortion can be achieved by early recognition of an infection and inflammation of the placenta and aggressive medical treatment," said Peter R. Morresey, BVSc, MACVSc, Dipl. ACVIM, ACT, an associate at Rood & Riddle Equine Hospital, in Lexington, Ky., during his presentation at the 12th Congress of The World Equine Veterinary Association, held Nov. 2-6, 2011, in Hyderabad, India.

According to Morresey, veteran mares that have foaled before are at a higher risk of developing a placental infection because they often have one or more anatomic defects in their reproductive tracts from previous foalings (involving the external genitalia) that allow opportunistic bacteria to be transferred from the vagina to the uterus through an incompetent cervix.

"Once the placenta becomes infected with bacteria, the fetal membranes become thick, which impedes the transfer of nutrients and gas exchange between the mare and foal," explained Morresey. "In addition, thickening of the placenta at the ‘cervical star’ (where the foal normally erupts through the placental membranes) can prevent rupture during delivery and compromise the health of the fetus, and bacteria can build up in this area and cause an infection in the neonatal foal