Foal Monitoring and Diagnostic Criteria

Beginning with the day of infection, rectal temperature, heart rate, and respiratory rate of the foals were monitored and recorded twice daily. Clinical signs of abnormal lung sounds, coughing, lethargy, respiratory effort, nasal discharge, and polysynovitis also were monitored and recorded twice daily. The lungs were monitored weekly using thoracic ultrasonography for evidence of peripheral pulmonary consolidation or abscess formation.

Foals were considered to manifest clinical signs of pneumonia when they had ultrasonographic evidence of pulmonary abscessation or consolidation with maximal lesion diameter ˃ 2.0 cm and either a rectal temperature of ˃ 39.7°C, a cough at rest, or both fever (˃ 39.7°C) and cough. On the day a foal was diagnosed with pneumonia, a CBC, thoracic ultrasonography, and T-TBA were performed. The T-TBA fluid was submitted to the Texas Veterinary Medical Diagnostic Laboratory, College Station, for cytologic examination and for microbiologic culture. Foals were considered to have a diagnosis of R. equi pneumonia if they met the aforementioned criteria for clinical signs of pneumonia and had cytologic evidence of septic inflammation with Gram-positive pleomorphic rods and R. equi recovered by microbiologic culture of T-TBA fluid. Foals were monitored through 84 days of age. Foals that did not have clinical signs of disease, but had ultra-sonographic evidence of lung lesions, were monitored through 84 days of age.