Heaves is a condition in horses that is characterized by inflamed airways in the lungs. It can lead to a number of related symptoms, such as chronic cough, excess mucous production, poor performance and weight loss. Heaves is also referenced by other names, including Recurrent Airway Obstruction (RAO), Equine Asthma, Equine Chronic Obstructive Pulmonary Disease, and Inflammatory Airway Disease (IAD).¹ Heaves is the most common respiratory malady affecting horses, with symptoms typically beginning at around 10 years of age.

The more intense symptoms of heaves (e.g., severe cough, labored breathing) can last for several days or weeks and are most often triggered by environmental allergens. These can also arise when horses are on pasture in hot, humid climates. 

The syndrome is analogous to asthma in humans and is a common reason for some horses persistently coughing. Several years ago, a consensus statement by the American College of Veterinary Internal Medicine proposed that these various syndromes be characterized under the term “equine asthma.”¹

The term “inflammatory airway disease” (IAD) has been used to describe the above when it presents in young horses; here, it is characterized by exercise intolerance and intermittent cough in horses that appear to be in normal condition at rest.  According to the available literature, these horses can recover completely with treatment; occasionally, such horses recover spontaneously.²

Equine Asthma Described

Recurrent airway obstruction (RAO, also known as heaves, broken wind or chronic airway reactivity) in horses is typically characterized by an overproduction of mucus, narrowing of the airway (bronchoconstriction) and bronchospasm. “Unlike IAD, horses with RAO are not normal at rest, and usually have an increased respiratory rate and/or cough.  The most common signs of RAO are chronic cough, nasal discharge, exercise intolerance, and respiratory difficulty. The classic ‘heave line’ that can be seen along the bottom edge of the ribs is due to hypertrophy of the abdominal muscles, which are assisting in breathing and become large from excess work.”¹ Severely-affected horses can also present with weight loss, anorexia, and exercise intolerance. Most affected horses do not run a fever unless a secondary bacterial pneumonia has occurred.

COPD causes horses to experience labored breathing and is often exacerbated during the winter. In many cases, COPD occurs in horses that have developed an allergic reaction to environmental dust allergens. The reaction causes inflammation and narrowing of the airways creating breathing difficulties. Usually, the affected horses are experiencing allergic reactions to environmental allergens such as fungal spores or pollen. These fungal spores are typically associated with dusty environments and bedding, or moldy hay and straw.² This is why COPD tends to be more common in stabled horses where dust and fungal spores are often prevalent.

Once a horse has developed an allergic reaction to such a substance, when the allergen is inhaled, the small airways of the affected horse are the most seriously impacted. The allergic reaction increases mucus production with inflammatory cells and constricts the airways through bronchospasm.^1,2 These conspire to reduce the airway diameter, thus making it harder for the horse to breathe. The airways can even completely collapse during expiration, making breathing out extremely difficult.

COPD is often associated with dusty environments and moldy hay. Its onset is usually gradual, with the initial signs often being imperceptible. As the allergy becomes established however, continuous exposure to the allergen leads to more attacks of greater severity.

Prevention and Symptom Reduction

Unless the veterinarian can determine a definitive cause at the outset of symptoms, the first thing the owner or manager will want to do is eliminate the variables that might be causing the horse’s distress. This means prevention, and prevention typically means cleaning and sound horse husbandry. 

The first step to reducing symptoms is to lower the dust level in the horse’s immediate environment. Regardless of the cause, this can improve breathing, since dust is a respiratory irritant that can build up in the lungs and block airways.² While keeping a barn dust-free is a near impossibility, allowing the horse to be outdoors as much as possible with a free-standing shelter is superior to stabling the horse as a matter of course. Horses should be indoors if the weather is too hot or cold of course, since extreme temperatures can exacerbate respiratory conditions.

If it is absolutely necessary to keep a horse in the barn for protracted periods of time, some of the literature suggests replacing hay and other bedding with rubber mats to reduce dust levels. In the barn, anything that can be done to provide the horse with fresh, clean air can make a significant difference in their breathing.

Dexamethasone Adverse Effects and Warnings

No serious adverse reactions have been reported for horses with dexamethasone given at normal doses.

The Association of Racing Commissioners International Uniform Classification Guidelines for Foreign Substances has designated dexamethasone a CLASS 4 DRUG.

Please consult your veterinarian prior to beginning any treatment regimen.

Where to buy Dexamethasone Powder

Dexamethasone is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies. 

Dexamethasone carries numerous potential drug interactions. Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

¹House, A. Recurrent Airway Obstruction (RAO) in the Horse. In: J. American Association of Equine Practitioners, Jan. 2016.

²Robinson, N.E. The Pathogenesis Of Chronic Obstructive Pulmonary Disease Of Horses. In: Br vet..]. (1996). 152, 283.

³Bazay, C. Dexamethasone Administration Routes in Horses Compared. In: The Horse, Jun 26, 2012.

⁵Notari L, Mills D. Possible behavioral effects of exogenous corticosteroids on dog behavior: a preliminary investigation. J Vet Behav. 2011;6(6):321-327.