Horses can “bleed” during or after intense work due to a condition called exercise-induced pulmonary hemorrhage (EIPH). This occurs when high blood pressure in the lung’s small blood vessels during strenuous exercise causes tiny vessels to rupture, allowing blood to leak into the airways or lung tissue. In many cases, visible nosebleeds are not always present; blood may be detected only by examining the airways or lung fluid after exercise. Key points to understand
- What happens anatomically: During intense exertion, the pulmonary capillaries experience very high transmural pressures from increased blood flow and negative pressures in the airways during inspiration. This stress can cause capillary walls to fail and bleed into the airways (alveoli and interstitial spaces) rather than through the nostrils in most horses.
- How common it is: EIPH is particularly common in high-performance horses (e.g., racehorses) but can occur in other sport horses that require sudden bursts of intense effort.
- How bleeding is detected: Visible nostril bleeding occurs in only a minority of cases; endoscopic examination after exercise often reveals blood in the airways. Diagnosis may include endoscopy or tracheal wash/bronchoalveolar lavage to assess airway blood and inflammation.
- Factors contributing to EIPH: Multiple factors are likely involved, including high pulmonary blood pressures, lung inflammation, structural fragility of the capillary walls, and mechanical stresses from airway flow and chest pressures during intense work. There is ongoing research, and management often targets reducing the severity of episodes rather than preventing all bleeding.
- Treatments and management: One pharmacologic intervention shown to reduce severity in some cases is the diuretic furosemide, which may lessen the extent of bleeding and improve performance during races, though it does not completely prevent EIPH. Other therapies have limited or mixed evidence. Environmental and training adaptations, plus veterinary guidance, are typically used to manage affected horses.
Practical takeaways for horse owners and handlers
- If a horse performs strenuous work and then shows nasal discharge that could be blood, or if there’s breathing difficulty after racing or intense training, this could be EIPH. A veterinarian should evaluate the horse to confirm whether blood is from the lungs and to rule out other airway or nasal causes.
- Regular performance horses may be screened or managed with tailored exercise plans and, in some regions, permitted pharmacologic strategies under veterinary supervision. Diuretic use (e.g., furosemide) is a common practice in some racing jurisdictions, but regulations vary and should be discussed with a veterinarian.
- Monitoring and prevention focus on minimizing peak pressures in the lungs during exercise, managing airway health, and addressing any underlying lung inflammation that could contribute to bleeding risk.
If you’d like, I can tailor this to a specific horse’s sport (e.g., racing, polo, endurance) and summarize the latest guidance from veterinary sources in that context.