Bleeding in the Racehorse

Bleeders, Allergies, Allergy Testing, Immunotherapy and the Racehorse

– A Study by H. O. Ferguson, DVM

Dr. Sam Ferguson of Ocala, Florida, is teaming up with interested racehorse trainers and owners to perform a scientific study and clinical trial exploring the possibility of an association between allergies and bleeding from the lungs (EIPH) in horses. Dr. Ferguson has worked on the track with and without the use of the current medication, lasix, and strongly feels that medication issues are a large detriment to the racing industry today. He also feels that in many instances our healthcare system looks for the income from a treatment, rather than research a cause of the problem. Following is a brief synopsis of EIPH (bleeding) and its possible correlation to allergies.

Exercise Induced Pulmonary Hemorrhage (EIPH) occurs quite commonly with some studies indicating up to a 60-70% incidence in the racehorse. The condition also occurs in other performance horses, man, and other animals. The cause is currently unknown, but one general consensus is that chronic airway disease leads to increased blood pressures (pulmonary hypertension) that subsequently lead to capillary rupture at maximal exercise. Studies have shown that furosemide (lasix) does indeed help prevent EIPH possibly by lowering the pulmonary blood pressures.

Allergies are basically an inappropriate immune response. They may be mild, for example, a skin rash, or severe enough to cause anaphylaxis and death. These reactions may be localized to the skin (e.g. hives), respiratory tract, other systems, or affect the whole animal. Although the exact causes of allergies are unknown, the ability to be allergic is thought to be highly heritable. Recent scientific epidemiological studies point to a logical, science-based explanation called the “Hygiene Hypothesis.” This somewhat explains the current epidemic-like conditions of asthma and bronchitis in highly civilized societies. Those who raise horses (and children) might research the concept more thoroughly. The basis for the theory is that we have down regulated certain allergic responses—and consequently immune responses—with “super-cleanliness” and an inherent lack of exposure in modern social environments. Allergies are not near as prevalent in third world countries.

One possible respiratory component of allergies is Chronic Obstructive Pulmonary Disease (COPD). COPD has been linked to pulmonary hypertension and may lead to bleeding at maximum exercise in people. COPD occurs in horses as well; hence, a possible connection between allergies and EIPH affected horses.

Allergy testing is primarily conducted in people and animals in two different ways. The older method involved skin testing and subjective analysis of the reactions produced to determine which allergens were most reactive. This is a cumbersome technique in that besides being a subjective analysis, medications can severely affect the outcome. The newer method is blood testing for allergen specific immunoglobulin (IgE). In this method, antibodies specific to particular allergens or allergic proteins are identified. From this, allergy “vaccines” are formulated and re-introduced into the animal to “immunize” or desensitize the animal’s allergic response. Most recently, as in humans, dogs, and cats, this can be done orally in the horse. This is called immunotherapy. It is highly unlikely that a specific allergen related to bleeders will be identified, but that effective immunotherapy will minimize the allergic response. In most instances, in the cases of true allergies, immunotherapy is 70-80% effective, though treatment may take several months or longer.

The Study–Objectives and Outline

The primary objective of the study is to correlate treatment of allergies with immunotherapy to a decreased incidence or severity of EIPH in horses. This will require a treatment population that has a significant bleeding issue; not the horse that runs on Lasix as a deterrent to bleeding or for other possible performance enhancing reasons. Obviously performance of the individual will be a key parameter in the study; and other reasons for bleeding will have to be considered, as well as other reasons for decreased performance.

The first step in the study will be the allergy testing.
This involves the collection of 5-6 ml of serum submitted to a lab with specific target antigens assessed. These target antigens are based on the regional location of the horse, as well as specific antigens related to his immediate environment. Examples would be tree pollens, dust mites, grasses and hays the horse is exposed to. This portion of the study will cost about $450. This includes lab costs, analyzing data for antigen selection, correlating all data, and administrative costs.

The second step in the study will be the immunotherapy.
After the specific antigens that seem most reactive and relevant have been selected, laboratory dermatologists formulate a specific prescription program for the horse, hopefully desensitizing his allergic response and alleviating low airway inflammation. A three-month supply will cost about $180.

The study has been protected with a provisional patent so that only one person can collect and correlate the data, Dr. Ferguson. This will hopefully minimize a free-for-all approach to this possibly successful therapy protocol; and significant scientific data can be collected. It will be important that all performance indicators for a horse are reported as this will be a significant parameter to success or failure of the therapy. Any significant examination results found by the attending veterinarian will need to be reported as well. Other performance findings, such as lameness or airway compromise, could potentially disqualify a horse from the study.

Depending on the number of horses that accurate tests and treatments are performed on, the study may last up to two years. First a certain population will have to undergo treatment, and then evaluation of treatment will have to be performed. As mentioned in the overview, treatment may take several months or longer.

Potential Side Effects

After administration of any medication, or any foreign protein, there is potential for side effects. Usually these are of no serious consequence in the horse. In addition, the testing involves very small amounts of antigen, and the immunotherapy is given sub-cutaneously, which alleviates some of the possibility of a bulk overload of the system. “Hives” is the most common allergic response seen. However, more serious side effects can happen, and all personnel will be trained with appropriate treatment for such events.

Basis of “Immunotherapy”

As mentioned in the overview, the body basically reacts to foreign proteins with the immune system which reacts with two sub-systems: Th1 cells and Th2 cells. The first seems to come in to play with viruses and bacteria; the second is more associated with other foreign proteins such as allergens. Immunotherapy seems to down-regulate an overly reactive Th2 reaction. Hence, even if a specific antigen is not used, the response level will be modulated to some degree. This whole concept is not fully understood and is controversial as well, because it would appear that testing with the specific antigens gives immunotherapy its best response. Therefore, in this study, we will make as good an attempt as possible to test specific antigens for that horse and the region he predominately races in.

To apply for treatment, download the Client and Patient Information Sheet and either email ( or fax (352-622-5663) the form to Dr. Ferguson. This will provide pertinent information in collection of allergens for testing as well as the specific clinical history of the horse.

Other Questions

Feel free to contact Dr. Ferguson’s office, preferably by email or fax.