Merck Manual

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Pet Owner Version

Exercise-induced Pulmonary Hemorrhage in Horses


Bonnie R. Rush

, DVM, MS, DACVIM, Equine Internal Medicine, College of Veterinary Medicine, Kansas State University

Reviewed/Revised May 2019 | Modified Oct 2022

Exercise-induced pulmonary (lung) bleeding occurs commonly in racehorses and is observed in horses used for other 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, lung inflammation, and shear forces within the chest generated during exercise. Research is ongoing, and the condition is likely due to multiple factors.

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 (guttural pouch mycosis and ethmoid hematoma) must be excluded during the examination. Examination of fluid collected from the lungs by inserting a tube through the nose and flushing saline into and out of 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 and improve race performance, although it does not prevent bleeding entirely. There is not strong evidence for the use of other drugs or interventions.

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