The cases of nocardioform placentitis in Central Kentucky fell from 144 cases during the 1999 foaling season to 48 in 2000, according to a report in Equine Disease Quarterly, a publication funded by Underwriters At Lloyd’s of London, Brokers, And Their Kentucky Agents. Prior to 1998, the Kentucky Livestock Disease Diagnostic Center diagnosed an average of 20 cases of nocardioform placentitis each foaling season. The apparent rise began with an increase to 94 cases in 1998, and researchers are unable to explain why these fluctuations occurred.

Placentitis is an inflammation of the placenta. Nocardioform placentitis is a distinct form of the disease diagnosed rarely outside of Central Kentucky. It is the most common cause of placentitis in Kentucky, outnumbering placentitis cases caused by leptospirosis and streptococcus.

Mares of all ages and breeds are affected, and might show no visible signs of disease. The mare might “bag up” early, which is a common sign of placentitis, but generally will not have vaginal discharge. Typically, a mare will abort in late gestation, have a stillborn or weak foal prematurely or at term, or can produce an apparently normal foal. The mare usually will rid herself of the bacteria rapidly after abortion or delivery, and future gestions don’t seem to be affected.

The distinct difference found with an affected mare is an area of the damage to the placenta. Neil Williams, DVM, PhD, said in the Equine Disease Quarterly that the placenta in nocardioform placentitis cases is characterized by an area of inflammation located on the cranial portion of the body of the placenta (near the top), often extending onto the area where the uterus joins the uterine horns. The affected area usually is large, but isolated. The surface of the placenta is covered with a thick, brown exudate, which contains dead placental cells, white blood cells, and bacteria