Equine Asthma – A Struggle to Breath

By Garrett Metcalf, DVM

Equine asthma has been known by many names over the years. It has been called, Chronic Obstructive Pulmonary Disease (COPD), Heaves, Inflammatory Airway Disease and Recurrent Airway Obstructions (RAO). Through research it has been shown that equine asthma in horses is more similar to human asthma compared to for example COPD. The semantics of the proper name of the disease is really not that important. Rather it is more important to identify and treat the disease properly to prevent episodes of heaves in possibly your own horse. But according to the American Veterinary College of Internal Medicine (ACVIM) the most proper term is equine asthma.

Equine asthma is commonly characterized as a person with COPD that you may see on commercials that say can get air in but can’t get air out. They often can inhale air more easily than expelling it on expiration. Horses can have a cough with equine asthma as well that can be common around mild amount of exercise, while eating or at times just at rest. Nasal discharge can also be present but no infectious agent is involved with equine asthma and horse will likely not have an elevated body temperature with equine asthma. Severe cases have can have serious difficulty breathing that is characterized as nostril flaring, heave line in the abdomen because of excessive abdominal force used to expel air, exercise intolerance, anorexia and weight loss.

There are two forms of equine asthma that is identified in horses. These different forms are barn-associated type and summer pasture-associated forms. Barn-associated form is often seen in horses that are wintered or stalled in a barn more frequently. Dust from barn aisle, shavings and also hay can be contributing triggers for horses with equine asthma. Summer pasture-associated form is often from allergens, pollens and molds that can be trigger for this form. It seems to be worsened by heat and humidity levels in the summer months compared to cooler times of the season.

Getting a diagnosis of equine asthma is not really all that difficult. Typically a physical exam with thorough auscultation of the lungs and history is adequate to make the diagnosis. It is often necessary to perform a re-breathing exam in horses to force the horse to take deeper breaths to hear the lungs more extensively. A re-breathing examination is performed by placing a 20-30L bag over a horses nose so that in re-breathes its own CO2 causing the horse to take deeper breaths while simultaneously the lungs are auscultated with a stethoscope.  In some cases more extensive testing is needed.  For example endoscopy is used to examine the trachea for evidence of tracheal inflammation and excessive mucous. BAL or bronchial alveolar lavage is used to sample fluid and cells from the deeper parts of the lung to confirm equine asthma and often is used in horses that display poor performance and coughing but not other obvious clinical signs. Thoracic ultrasound and x-ray can be useful tools as well to confirm the disease in some cases and also rule out other serious diseases especially in cases that fail to respond to standard therapies for equine asthma.

Often the diagnosis is straight forward but rather the more difficulties lie in being able to control and prevent the disease from occurring in horses. First off the number one step is to identify and try to eliminate the triggers from the horse’s environment. The most common culprit of triggering heaves is round bale hays. Round bales are convenient ways of feeding hay roughage but are also great sources of mold, pollen and dust. Often horses eat holes in the hay bales creating a tunnel that just baths the horse in hay dust and mold which is inhaled into the airway. Often to further eliminate dusts, pollen and molds from hay is by wetting it down to prevent aerosolization of the particles that can trigger equine asthma. In horses that have barn-associated asthma then are often better off on clean green grass as a feed source and out of a stall. Summer pasture-associated asthma cases need to be dry lot with hay and pellet feeds for a diet with dust control as needed.

Read more in the December 2020 issue of Oklahoma Farm & Ranch.