Pleuritis secondary to pneumonia or lung abscessation in 90 horses

Of 122 horses with pleural effusion, 90 (73.8%) had pleuritis secondary to pneumonia or lung abscessation. Fifty-one horses died or were euthanatized. The highest prevalence was in Thoroughbred and Standardbred racehorses. Eleven (12.2%) horses were postsurgical patients and 22 (24.4%) horses had been transported over 500 miles. There was no relationship between final outcome and the age, sex, breed, hematologic values, or laboratory findings pertaining to pleural fluid except for the bacterial isolation of Escherichia coli from the pleural fluid, as this was more frequently associated with death. Follow-up on 38 of the 39 horses that survived showed that 18 (46.2%) recovered and were able to return to performance equal to that prior to their illness. Ten (25.6%) were returned for breeding or pleasure use, with no attempt made to return them to racing. Follow-up was not available for 5 horses, 4 horses had just recently been discharged from the hospital, and 2 horses are racing poorer than prior to their illness.