One of the major foal diseases in the United States is Rhodococcus equi foal pneumonia. Responsible for the deaths of up to 30% of infected foals, it is a serious problem at many large breeding farms. Noah Cohen, VMD, MPH, PhD, Dipl. ACVIM, professor of Large Animal Clinical Sciences at Texas A&M University’s College of Veterinary Medicine & Biomedical Sciences, presented a study on the epidemiology (“scientific discipline concerned with quantifying the distribution of disease and determinants of disease and health in populations “) of R. equi at the 2010 American Association of Equine Practitioners Convention, which took place Dec. 5-8 in Baltimore, Md.

In his presentation, he reviewed published research about why some foals contract R. equi pneumonia in the same environment where other foals do not, and why R. equi is more prevalent at some farms but virtually nonexistent at others.

According to Cohen, virulent (disease-causing) R. equi has been isolated from several sources on breeding farms including feces (from both foals and their dams), horse feed, the soil, and the air. Especially at farms with high concentrations of foals, Cohen says it’s likely that all foals are exposed to the disease-causing bacterium, but only a small portion of foals actually contract pneumonia.

He noted in the study that the concentration of virulent (disease-causing) R. equi in the dams’ feces was not related to the risk of a foal developing pneumonia caused by the bacterium; in other words, mares shedding more R. equi in their feces did not appear to explain the disease. However, that study also observed that nearly all mares shed virulent R. equi in their feces during the period shortly after birth of foals