Exercise-induced pulmonary (lung) bleeding occurs in the majority of racehorses and is observed in many other equine sports (such as polo, barrel racing, and 3-day events) that require strenuous exercise for short periods of time. Bleeding from the nose is actually observed in only about 5% of horses with exercised-induced lung hemorrhage; however, examination of racehorses has shown that bleeding in the airways is present in a majority of horses.

Possible causes include high lung blood pressures during intense exercise, new blood vessel formation caused by lung inflammation, and shear forces within the chest generated during exercise. Some research suggests that exercise-induced lung hemorrhage results from failure of the horse's lungs to accommodate the massive increase in heart output to meet the demands of high-intensity exercise.

Diagnosis of exercise-induced lung hemorrhage involves observation of blood in the airways 30 to 90 minutes after exercise. This can be detected using an endoscope. Other sources of bleeding in the upper airway must be exluded during the examination. Examination of fluid from the lungs is sometimes used if the horse cannot be examined after exercise.

The use of a specific diuretic drug, furosemide, can reduce the severity of exercise-induced lung hemorrhage by 70% and improve race performance, although it does not prevent bleeding entirely. Nasal dilator bands also appear to reduce bleeding by approximately 30%.

Last full review/revision July 2011 by Bonnie R. Rush, DVM, MS, DACVIM; Neil W. Dyer, DVM, MS, DACVP; Joe Hauptman, DVM, MS, DACVS; Ned F. Kuehn, DVM, MS, DACVIM; Stuart M. Taylor, PhD, BVMS, MRCVS, DECVP; Wendy E. Vaala, VMD, DACVIM; Maureen H. Milne, BVMS, MVM, DCHP, MRCVS