🐴 Bleeding in the Lungs of Endurance Horses: Understanding EIPH in 2025 🫁💥

By Dr Duncan Houston BVSc

Exercise-induced pulmonary hemorrhage (EIPH)—or lung bleeding during intense exertion—is a well-known issue in racehorses. In fact, studies show up to 90% of racehorses exhibit some form of EIPH after competition. But what about endurance horses? In 2025, new evidence reveals that this problem may be more widespread in endurance disciplines than previously thought. 🧠🐎

🫁 What Is EIPH?

EIPH occurs when intense physical exertion causes small blood vessels in the lungs to rupture. This releases blood into the airways, especially the trachea and bronchi. The result?

• 🩸 Airway inflammation and irritation
• 💨 Reduced oxygen exchange
• 📉 Decreased athletic performance

In racehorses, EIPH is a diagnosed performance-limiting factor. Until recently, it was less studied in other disciplines like endurance racing. 🔬

🔬 The Study: EIPH in Endurance Horses

A Spanish research team conducted a study on 20 endurance horses. Findings showed:

• 📉 65% had evidence of EIPH
• 📆 Bleeding was detected 3–8 days and even 36–38 days after a race
• 🩸 50% still showed evidence of EIPH over 30 days post-event

This prolonged presence of blood is unusual and raises concern about chronic airway damage in endurance athletes. 🧬

🔍 How Is EIPH Diagnosed?

There are two main methods:

✅ 1. Tracheal Endoscopy

• 🔬 A scope is passed into the trachea to visualize bleeding
• 💯 Useful for identifying moderate to severe bleeding

✅ 2. Cytology of Tracheal/Bronchoalveolar Lavage

• 🧪 Fluid is collected from the lower airways
• 🔍 Cells are examined microscopically for red blood cells or hemosiderin

Combining both methods improves diagnostic accuracy—especially for subclinical or low-grade bleeds. 📸

📉 Does EIPH Affect Endurance Performance?

This remains an open question. While EIPH is linked to slower times and poor performance in racehorses, the same connection hasn't been definitively proven in endurance horses yet. ❓

However, given the long recovery periods observed in the study, chronic inflammation or scarring in the lungs is likely to affect:

• 💨 Respiratory efficiency
• ⏳ Recovery times between stages or competitions
• 📈 Risk of complications such as respiratory infections

🚫 Why Furosemide Isn’t Used in Endurance Horses

Racehorses with EIPH are often treated with furosemide (Lasix)—a diuretic that reduces pulmonary blood pressure. But in endurance horses:

• 💧 Furosemide increases dehydration risk
• 🌞 This is especially dangerous in long-distance events where fluid loss is already high

As a result, there is currently no approved treatment to prevent EIPH in endurance horses. ❌

🧠 What Can Be Done?

📋 1. Pre-Event Screening

• 📅 Schedule a tracheal endoscopy post-event for endurance horses with performance issues
• 🔍 Look for signs of blood, airway scarring, or inflammation

💨 2. Optimize Respiratory Health

• 🧼 Keep stables and trailers well-ventilated
• 🚫 Avoid dust and mold in hay and bedding

📉 3. Monitor Recovery Post-Race

• 📈 Monitor respiratory rate and effort for 48–72 hours post-event
• 📸 Watch for nasal discharge or coughing

🛠️ 4. Research-Based Innovations

• 🔬 Future therapies may include pulmonary conditioning or targeted supplements
• 🧪 Studies are ongoing to identify safe EIPH preventatives for endurance horses

📲 Ask A Vet for EIPH Evaluation

If your endurance horse shows unexplained fatigue, slow recovery, or respiratory issues, visit AskAVet.com or use the Ask A Vet App to schedule an airway evaluation. 📱🐴

Dr Duncan Houston and the team can help coordinate endoscopy, interpret lab results, and provide science-based training advice for lung health. 💬🧠

🏁 Final Thoughts

EIPH isn’t just a racehorse problem—it’s becoming recognized in other disciplines, including endurance. In 2025, while no perfect treatment exists, early diagnosis and lung protection strategies can make a meaningful difference in performance and longevity. 🫁🐎

Concerned about lung health in your performance horse? Visit AskAVet.com for tailored respiratory care 🐴💨