Understanding Exercise-Induced Pulmonary Hemorrhage (EIPH) in Horses

EIPH is a condition that affects horses involved in high-performance activities like racing and barrel racing.  It’s commonly seen as bleeding from the nostrils, or finding blood in the throat (trachea) via endoscopic exam.  Let’s take a look at what’s happening beneath the surface to understand why it happens, and how to manage it.

Why do horses bleed, or what causes EIPH?

When horses push their limits during intense exercise, tiny blood vessels in their lungs can burst, leading to bleeding. This happens due to the strain on their breathing and circulation systems, which work overtime during high-intensity activity.

1. Breathing and Movement Mechanics

Horses have a unique way of breathing in sync with their strides when running. This forces air into their lungs before they’ve had a chance to fully empty, creating extra stress on delicate lung tissues.

2. High Blood Pressure in the Lungs

Horses are built for speed and endurance, which means their bodies pump a massive amount of blood during exercise. The high pressure in their lung blood vessels can make these vessels stretch to capacity.  When distended, they become less flexible, and break under stress.

3. Blood Becomes Thicker

During exercise, a horse’s spleen releases extra red blood cells to improve oxygen delivery. While this helps with performance, it also thickens the blood, making it harder for vessels to stay flexible, increasing the risk of rupture.

4. Lung Damage over Time

When EIPH happens repeatedly, the damaged areas heal with scar tissue. This scar tissue isn’t as stretchy or efficient for oxygen exchange, making the lungs more prone to future bleeding.

5. Stride Problems from Lameness

If a horse is injured or lame, it can disrupt its natural stride, which can also throw off its breathing rhythm. This adds to the stress on the lungs and raises the chance of EIPH.

How can EIPH be prevented?

While EIPH can’t always be completely avoided, there are ways to reduce the risk:

1. Build Fitness Slowly

A gradual approach to fitness gives a horse’s heart, lungs, and blood vessels time to adapt to the increased workload. This helps lower the strain on their pulmonary system.

2. Medications

Some horses are given furosemide (a diuretic) to lower blood pressure in the lungs and reduce the risk of bleeding. However, regulations on its use are tightening, and it may eventually be banned in some jurisdictions.

3. Nutrition

Supplements like L-citrulline and L-arginine may help by relaxing blood vessels and airways. Herbal remedies are sometimes suggested too, but there’s not much scientific evidence to back them up.  They do have some supporting anecdotal evidence in their favor, however.

Helping a horse recover from EIPH

If a horse does experience EIPH, it’s important to support healing and prevent further damage:

1. Rest and Recovery

Avoid intense exercise while the lungs are healing. Damaged tissue is fragile and more likely to bleed again if stressed too soon.

2. Medical Treatments

Some veterinarians use treatments like DMSO therapy to reduce scar tissue formation. Hyperbaric oxygen therapy can be very effective speeding healing time and preventing/managing infection.

3. Support with Supplements

Certain supplements might help the lungs heal by supporting healthy tissue and blood vessel formation, though the science on this is still developing.

Final thoughts

EIPH is a complex condition tied to the unique physiology of horses and the demands of their athletic performance. Prevention starts with proper fitness training, smart use of medications, and nutritional support. If EIPH does occur, giving the lungs time to heal and using medical interventions can make a big difference. Understanding and managing EIPH can help horses stay healthy and perform at their best.