Summer pasture-associated obstructive pulmonary disease in horses: 21 cases (1983-1991).

Medical records of 21 horses with summer pasture-associated obstructive pulmonary disease were reviewed, and history, signalment, clinical signs, radiographic signs, clinicopathologic data, and therapeutic response were determined. Most affected horses were used as pleasure horses, and for the most part, remained at pasture when not in use. The mean age (+/- SD) was 13.7 +/- 3.6 years. Clinical signs included intermittent nasal discharge, cough, tachypnea, labored expiratory effort, and crackles and wheezes on auscultation. Radiography frequently revealed interstitial patterns in the lung fields; in horses with chronic disease, pulmonary overinflation was evident. Hemogram was usually normal, and transtracheal wash fluid was characterized by nondegenerate neutrophils.