Placentitis is a common cause of late-pregnancy abortion in mares and poses a significant threat to fetal and neonatal viability. Bacterial agents commonly associated with the occurrence of placentitis include Streptococcus equi subspecies zooepidemicus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Leptospira spp, nocardioform bacteria (Crossiella equi, Amycolatopsis spp) and others.

Except for leptospiral and nocardioform placentitis, most cases of bacterial placentitis are thought to originate due to bacterial invasion via the cervix. Therefore, these cases of ascending placentitis usually start at the cervical star (where the foal normally erupts through the placental membranes) and spread from there. Infection of the placenta results in subsequent infection of the fetus and in the release of prostaglandins from the inflamed placenta, which ultimately leads to abortion or delivery of a premature foal with bacterial sepsis.

Effective treatment of placentitis requires early diagnosis prior to the appearance of clinical signs, such as premature udder development with or without the streaming of milk and/or vulvar discharge.

Currently, ultrasonographic evaluation of the placenta is used to detect early cases of placentitis and to implement treatment to prevent abortion and delay premature labor. While this practice has allowed more effective treatment and has improved the outcome in many cases, it is often not practical to ultrasound every mare repeatedly during late gestation. In addition, early stages of placentitis can be missed during ultrasonographic exam