Bleeding in the lungs is caused by excessive vigorous exercise.
When a horse runs, a large impact force is transmitted through their front legs to the shoulder blades and chest wall into the lungs. The faster the horse is running, the greater this force resulting in more damage and bleeding in the lungs and airways.
Using an endoscope inserted into the horse’s throat, researchers at the University of Melbourne have shown that 50% of racehorses have blood in their windpipe, and 90% have blood deeper in their lungs.
Horses over 5 years old are more likely to have haemorrhaging, possibly because the lungs cannot repair damage during continued training and over the years, the problem becomes chronic.
Between 1% and 2% of horses have blood flowing from the nostrils after a race. The first time this happens they are banned from racing for 3 months, the second time they are banned for life.
A study in the Equine Veterinary Journal found hemorrhaging in the lungs in 95% of horses checked during two post-race examinations
(Birks EK, Shuler KM, Soma LR, Martin BB, Marconato L, Del Piero F., Teleis DC, Schar D., Hessinger AE, Uboh CE, “EIPH: postrace endoscopic evaluation of Standardbreds and Thoroughbreds,” Department of Clinical Studies, University of Pennsylvania, Equine Veterinary Journal Supplement, September 2002).
Another article states that hemorrhaging in the lungs is “a condition affecting virtually all horses during intense exercise worldwide….there is no treatment that is considered a solution, and the currently allowed treatments have not proven to be effective….”
(Birks EK, Durando MM, McBride S., “Exercise-induced pulmonary hemorrhage,” Sports Medicine and Imaging, Department of Clinical Studies, University of Pennsylvania School of Veterinary Medicine, Veterinary Clin North America Equine Pract, April 2003).