Pleuritis and pleural effusion in the horse: a study of 37 cases.

Pleural effusion in 37 horses, including 15 acutely affected and 22 chronically affected, was found to be due to a variety of causes, including lymphocarcoma, pulmonary granulomas, coccidioidomycosis, equine infectious anemia, pulmonary abscesses, chronic pneumonia, and primary septic pleural effusion. Age, breed, or sex predilection was not found. Horses with chronic disease had weight loss, increased respiratory rate, dull respiratory sounds in the ventral portion of the thorax, and varying degrees of anorexia. Many horses were anemic. Those acutely affected had respiratory distress or signs of colic and many were anorectic. Most horses with acute primary disease had small volumes of pleural fluid. Culture and cytologic examination of pleural fluid and tracheal washings revealed the causative organism in some instances, but in a number of "primary" cases there were negative results on bacterial culture. The latter cases must be differentiated from other causes of chronic weight loss in the horse.