A 5-yr-old male Quarter horse is brought to the clinic by his owner. For approximately 1 mo, the patient has had an abscess in his left pectoral region, suggestive of Pigeon fever. In the last week, the patient has had temperatures up to 40° C and has a deep moist cough. He has been treated at home with oral phenylbutazone (unknown dose) for the fevers. A mobile veterinarian examined the patient in the past week and noted increased airway sounds. The horse was referred to the clinic for further evaluation.