A study of one Lexington, Ky., Thoroughbred farm showed that on average, 30% of the farm’s foals developed Rhodococcus equi pneumonia during the 2004 and 2005 foaling seasons. Researchers searching for a source of the disease questioned if R. equi in the mare’s feces was a source of infection for her foal. Information from this study was presented at the 2006 AAEP Convention.

They found that all mares at some point post-foaling shed R. equi in their feces. This meant that screening mare feces for R. equi to help control the spread of the disease would be a waste of time.

Noah Cohen, VMD, PhD, MPH, Dipl. ACVIM, associate professor at Texas A&M University’s College of Veterinary Medicine, said, “In either year, virulent R. equi was isolated from the feces of every mare in the study at one or more sampling times (there were four sample times),” Cohen explained. “One-third of the mares were shedding R. equi in all four of those samples.” He added that 80% of the mares were positive in three or more samplings.

“Fecal concentrations of total or virulent R. equi were not higher in mares whose foals developed R. equi than in those whose foals were unaffected,” Cohen said. “If this is true at other farms, screening mares for fecal concentrations cannot be used to help control R. equi pneumonia