Prevention of foal mortality due to Rhodococcus equi pneumonia on an endemically affected farm

Over the course of one summer, foals on a horse breeding farm where Rhodococcus equi infection was endemic were examined clinically twice weekly for evidence of R. equi pneumonia. Examination usually commenced from the week of birth and continued for up to 14 weeks of age. Affected animals were treated with a variety of antimicrobial drugs and such treatment was often prolonged. For descriptive purposes, we regarded a foal as developing R. equi pneumonia if the rectal temperature rose above 39 degrees C, the respiratory rate was over 40 per min, there were characteristic associated changes in respiratory sounds on auscultation, and the foal responded to antimicrobial treatment. In a group of 16 foals followed in this way, R. equi pneumonia developed in at least 14. Seven of these foals developed antibodies to equi factors as determined in a neutralizing antibody assay. Mean age of onset of these 14 foals was 3.4 weeks. Three foals developed the disease between 1.5-2.5 weeks of age, and 12 of 14 before four weeks of age. In previous years four to six foals died on the farm each summer of R. equi pneumonia; only one foal died of R. equi pneumonia on the farm during the summer of this study, and this foal did not form part of the study group. Early clinical recognition and treatment of R. equi pneumonia in foals on endemically affected farms may be an effective way to prevent deaths due to this infection.