Equine asthma is the most common non-infectious respiratory disease occurring in adult horses. The disease was called heaves or COPD but is now called asthma. It’s believed to be related to allergies caused by organic dust in the bedding and feed as well as the concentration of ammonia in horses’ stalls. Several different organic compounds have been found in stable dust, including bacterial endotoxins, over 50 different species of molds, storage mites, and plant particles. It seems mold spores are the cause of an allergic reaction leading to symptoms of asthma such as labored breathing and coughing.

Veterinary researchers in Germany worked to find which specific allergens contributed to the disease to develop a serum to desensitize horses to the allergen and decrease the reaction. To determine the cause of the reaction, the researchers tested six horses without a history of respiratory disease and nine horses with equine asthma. Four different allergy tests were used on all horses including blood tests, skin tests, and inhalant tests.

Unfortunately, there was no agreement among the tests as far as figuring out the specific cause of the allergy. Positive results on one test were negative on others, and tests on the normal horses showed positive. It is believed that positive skin tests may be related to local reactions of skin cells which do not correlate with allergies in the respiratory tract. The same problem has been discovered in human medicine with skin testing. Because of this, allergy testing is unlikely to be helpful in the diagnosis and treatment of horses with asthma.