Foal-Level Risk Factors Associated With Development of Rhodococcus equi Pneumonia at a Quarter Horse Breeding Farm

Abstract The occurrence of Rhodococcus equiat farms varies, with disease occurring endemically at some farms, but only sporadically, or not at all at other farms. Only some foalsresiding on endemic farms develop clinical signs of disease. Limited evidence is available regarding foal-level risk factors for the development of R. equi pneumonia. The purpose of this study was to identify foal-level risk factors associated with the development of R. equi pneumonia among foalsat a large breeding farm in Texas with a recurrent problem of R. equi pneumonia. A retrospective cohort studywas conducted using data from foalsborn at the farm from January 2009 through December 2011 that met the criteria for inclusion. Dam-level, foal-level, and health-related data were collected from all foals. Independent variables were analyzed with logistic regression, controlling for the effect of year. Data from 787 foalsborn at the farm were included, of which 209 (27%) developed R. equi pneumonia. The cumulative incidenceof disease at the farm varied significantly by year. Foalsthat were diagnosed with a prior morbidity besides R. equi were less likely to develop R. equi pneumonia.