One of the most widely recognized of all disorders affecting race horses, performance horses and other working horses, is “bleeding,” or exercise-induced pulmonary hemorrhage (EIPH). We now know that most racehorses bleed at some time during their careers. In fact, many horses might bleed every time they undertake intense exercise. Bleeding can occur in situations other than just flat racing. For example, EIPH has been detected in three-day eventers, steeplechasers, polo ponies, and other performance horses. Bleeding has even been observed in draft horses pulling heavy loads. The common denominator is strenuous exercise.
EIPH has been recognized for more than 300 years. Research in the last 20 or so years has shed some light on why horses bleed during strenuous exercise, But even still, there is no consensus regarding the true cause of EIPH.
What Exactly is EIPH?
EIPH refers to the breaking of blood vessels in the lungs as a result of exercise. The blood enters the airways and is then moved from the smaller to the larger airways and eventually is propelled by the cilia of ciliated epithelial cell (small hairs on the cells that line the airways that beat and move mucus and debris) up the trachea (windpipe). In most cases the blood is swallowed and never seen unless the horse is ‘scoped. For most horses the amount of blood that enters the airways is small. This is because the blood vessels that are rupturing are some of the smallest in the lung. This is where the blood vessel wall is around 1/100th the thickness of a human hair. The wall has to be this thin to allow oxygen to pass easily from the air spaces into the blood. In a much smaller number of cases larger blood vessels rupture and the amount of blood that enters the airways is too much for the horse to swallow and it appears at the nostrils. This may look like ordinary blood or it may have a pink and foamy appearance.
What Causes Blood Vessels to Break?
EIPH can be due to a number of different things that happen during exercise.
How Common is EIPH?
ALL horses break some blood vessels when they exercise at or above an intense trot. However, at the lower level this bleeding does not show in the trachea. Most studies have therefore assessed whether horses have bled or not based on endoscopy and scoring of blood seen in the trachea after exercise. This can be thought of as more severe and more significant bleeding, in health terms. Studies have shown that if a racehorse is scoped once after racing, between 40 and 80% will show some blood in the trachea. However, if a racehorse horse is ‘scoped on 3 different occasions it will show blood in the trachea at least once.
The prevalence of EIPH assessed by 'scoping' horses has been found to be:
How Is EIPH Diagnosed?
If your horse has blood at the nostrils after exercise the chances are this is probably but not always coming from the lungs. However, the majority of horses do not show blood at the nostrils after exercise. The most common way to assess EIPH is by endoscopy. This is usually done 30-40 minutes after exercise as it takes this long for blood to move from the periphery of the lung into the trachea. The amount of blood visible is most commonly scored on a 4 point scale (0= no visible blood to 3 = more than half the trachea covered with blood).
It's common for many low and intermediate level bleeders to show no symptoms of lung bleeding; however symptoms include:
What are Treatment and Management Options?
Epistaxis is always a concern and you should contact your vet if this happens. Sometime the bleeding comes from the upper airways (in the head) and may not be related to the lungs at all. This can occur because the horse has bashed its head or because of a fungal infection. For more common endoscopic (i.e. not visible) EIPH, Lasix (furosemide) is commonly given, although recent research shows this becomes less effective the more it is used. Lasix is given 4 hours before exercise, which increases urine output and thus reduces blood volume. In this way it has been shown to reduce calculated pulmonary capillary blood pressure and transmural pressure. Lasix has been shown to reduce EIPH severity in a treadmill study, however it does not completely prevent EIPH occurring.
Another alternative which has good scientific evidence is Flair equine nasal strips. For horses that are bleeding more severely due to atrial fibrillation, this can be treated with the drug quinidine or by electrical stimulation of the heart via catheters.
Some studies have also reported bioflavonoids having a benefit in conditions involving capillary hyper-permeability. Additionally the formulation contains vitamin K for its role in blood coagulation and to assist in this blood clotting in the event of an EIPH episode.
Maintaining good respiratory health also likely to reduces the severity of EIPH as any degree of inflammation within the airways will only add more stress on the respiratory system. One of the most common avoidable causes of airway inflammation and respiratory disease is exposure to respirable dust from your horse's environment and in particular from their forage.
Article information and inspiration from the following sources:
More Scientific articles about EPIH here: