Exercise-Induced Pulmonary Hemorrhage

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Diseases and conditions image EquiMed

Also Known As

Bleeder disease, EIPH, Epistaxis


Exercise induced pulmonary hemorrhage (EIPH), or bleeding in the lungs, occurs when blood enters the air passages of a horse's lung. According to one widely accepted theory about the cause of EIPH, high blood pressure from heavy exercise, coupled with vacuum-like effects during deep inhalation, causes capillaries to rupture and release blood into the throat and nostril passageways of the horse leading to blood seeping into the horse's lungs.

Another theory which explains the presence of bleeding in the upper back lobes of the lungs relates to the anatomy of a running horse. A horse's forelegs are not attached to the spine by bony structures. The action of running causes the shoulder muscles to compress the rib cage. The resulting wave of pressure spreads outward causing a shearing force on the tissue in the upper back of the lungs, resulting in bleeding.

This bleeding is similar to blunt force trauma because the bleeding does not occur at the location of the trauma; instead, it occurs on the opposite side of the body.

An additional theory relates to weakened capillaries because of inadequate nutrition. Many horses have thick, toxic, poorly oxygenated blood due to exposure to chemicals and drugs. This causes the heart to work harder and the blood pressure to rise with the resulting increased arterial blood pressure breaking through capillary walls.

There are also schools of thought related to the evolutionary standpoint that horses were not designed to race or run. Horses were designed to graze and travel for miles at a walking pace. They would sprint only to outrun a predator. According to some theorists, when we, as humans, force horses to race or participate in heavy exercise, their hearts and lungs break down and bleeding occurs.


  • Blood flowing from one or both nostrils
  • Evidence of a trickle of blood-tinged mucus from the nose, or traces of blood on the feed bin in the 24-36 hours following a race
  • History of one or more good performances followed by loss of form in subsequent competition
  • A whistling or roaring that can be heard when a horse is breathing deeply from exertion.
  • Abnormal or choking sounds during sustained exercise
  • History of slow recovery and reluctance to put forth effort for 3 - 4 days after a hard race or work out
  • Horse unable to sustain its all-out speed and drops back when pressed hard
  • Lost stride rhythm and 'tongue over the bit' when pressed to run to the finish line
  • Horse appears distressed and uneasy, and swallows repeatedly within 15-30 minutes of a race


Bleeding appears to be related to the speed of exercise with greater risk in horses exercising at maximum speed and effort. Recent research shows that pulmonary artery blood pressure increases dramatically during heavy exercise because of the need for oxygen by the rapidly contracting muscles.

Once a few blood vessels burst, the blood in the air sacs reduces surface tension and more capillaries are likely to rupture.

According to one important theory, locomotory impact can produce lung tissue damage resulting in localized bruising and bleeding from the lungs.

Many other factors may contribute, including age of the horse, airway inflammatory conditions, small airway disease, capillary pressure within the lungs, track surface, training methods, and body and lung conformation.


Preventing recurring episodes of 'bleeding' is important in keeping a horse healthy. The environment should be studied carefully, making sure that there is plenty of ventilation to provide fresh, clean air. Exposure to fungus, mold spores and other potential allergens should be avoided, and hay should be of good quality and without contaminants.

Horse stalls should be mucked out regularly to avoid possible exposure and irritation by ammonia from urine in the bedding. If possible the horse should be turned outdoors for as many hours as possible.

Some veterinarians believe that three areas influence the high pulmonary blood pressure: the pulmonary blood vessels, the heart, and the spleen. Research is currently being done to find out if the problem occurs because of the heart, or whether it is a problem with the lungs.

Bleeding may be related to the structural efficiency of the lungs and the amount of scarring from previous bleeding episodes. According to researchers, each horse should be treated as an individual with training and conditioning to make the horse stronger and more fit before strenuous activity. Exercise and conditioning programs should be geared toward the horse becoming more fit in a step-by-step way and over-doing exercise that may lead to internal bleeding should be avoided.

Some vets also believe that diets high in protein in the form of alfalfa hay may be a contributing factor to bleeding in the lungs. When excess protein is broken down into urea that is expelled in urine and the ammonia fumes are inhaled over a period of time by the horse, it causes irritation in the airways and lungs, causing them to bleed when exercised at a high level.



Feeding the horse in a natural grazing position with head and neck lowered to eat is important. When horses feed from feeders that are at eye level, they inhale spores and dust from the hay which can irritate airways and lungs. Paying close attention to the horses environment, exercise program, and diet will pay off with better all-around health.


EIPH is rarely fatal, but can be very serious and costly to treat. Giving the horse that has problems with bleeding a diuretic called furosemide (Lasix) before a race, reduces the high blood pressure, but doesn't completely eliminate the problem. If over used, the horse may become dehydrated, develop electrolyte imbalances and experience a low potassium level, which may require that the horse receive supplements.

Complete recovery from a bleeding episode may take four to six weeks. In many states and countries a horse cannot race for at least 10 days after a bleeding episode.

A relatively new technique, bronchoalveolar lavage or lung wash can help confirm the relative severity and frequency of previous bleeds deep within the lungs. The lung air sacs and airways are washed and a sample is drawn back into a syringe for laboratory analysis.

A blood test may show an increase in bilirubin bile pigment readings and a reduced red cell count indicating loss and breakdown of red cells. Horses that are shown to be severe hidden bleeders through these tests should be give two to three months rest before returning to training to prevent permanent lung damage and an increased risk of bleeding problems in the future.

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