Frequency of Rhodococcus equi in Feces of Mares in Central Kentucky

Rhodococcus equi (R equi) pneumonia is an important cause of disease and death in foals. Feces from mares can contain R equi, including virulent R equi, and thus may act as a source of the bacteria at horse breeding farms. A previous report documented that every mare at a farm in central Kentucky shed virulent R equi in at least one of four fecal samples collected serially during the periparturient period. The objective of this study was to assess the extent to which this high prevalence of fecal shedding could be replicated at other horse breeding farms. The frequency of detection of R equi and virulent R equi in fecal samples was studied among 131 mares from 24 farms in central Kentucky. The proportions of fecal samples from mares containing R equi and virulent R equi were 95% and 76%, respectively. These findings indicate that R equi and virulent R equi may be isolated with high frequency from feces of mares at breeding farms in central Kentucky, and that mares are a source of virulent R equi for the environment of their foals.