Several conditions can threaten pregnancy in the late gestational mare. C.S. Bailey, DVM, who is completing a theriogenology residency at the University of Florida and Hagyard Equine Medical Institute in Lexington, Ky., said some of these conditions might warrant the use of therapeutic agents, in spite of limited knowledge about their efficacy or their ability to penetrate fetal membranes.

Current information regarding the effects of antibiotics and anti-inflammatory agents in the gravid mare is based on a model of experimentally induced placentitis in the research setting, added Bailey in his presentation at the Hagyard Bluegrass Equine Reproduction Symposium 2006, which was held Oct. 18-21 in Lexington, Ky.

In the United States, placentitis is considered a leading cause of abortion and neonatal loss, accounting for nearly a third of documented cases. Mares at risk for placentitis include those with poor perineal conformation, a previous history of placentitis, and multiparous mares (those that have had several foals). Three major types of placentitis are recognized in this country, including ascending bacterial placentitis, nocardioform placentitis, and placentitis associated with mare reproductive loss syndrome (MRLS).

Placentitis is commonly caused by bacterial infection ascending through the cervix, with Streptococcus equi subspecies zooepidemicus most frequently implicated. Typically, diagnosis is based on clinical signs and ultrasonographic findings. At present, most successful treatment regimens include a combination of antibiotics, anti-inflammatory drugs, and tocolytic (labor-inhibiting) agents