Recurrent airway obstruction (RAO) a name given to a frequently-occurring respiratory disease syndrome that affects horses. It is also known as chronic obstructive pulmonary disease (COPD) and “heaves.” The syndrome is analogous to asthma in humans and is a common reason for some horses persistently coughing. Suffice it to say that a number of terms and acronyms have been used over the years for the variety of inflammatory airway conditions causing cough and respiratory distress in the horse. 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 syndrome 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. 

RAO and COPD in Horses

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.

As with humans, 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 mouldy hay and straw.2 This is why COPD tends to be more common in stabled horses where dust and fungal spores are often prevalent.

It is important to remember that like humans, horses can develop allergies to substances they once tolerated well. 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 usually affects older, stabled horses, but it can occur in a horse of any age and in horses at pasture. While not always the case, COPD is typically 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.

Eliminating the Variables

Unless a definitive cause can be determined at the outset of symptoms, the first thing the horse owner or stable 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 (or sounder) horse husbandry. 

The first step to reducing symptoms is to lower the dust level in the horse’s living quarters. 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 make any respiratory condition worse.

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 / Dexamethasone Sodium Phosphate

Dexamethasone is a glucocorticoid medication that is available in injectable, oral, and ophthalmic forms. It is long acting, and 30 times more potent than hydrocortisone with no mineralocorticoid activity.4 Contraindications include systemic fungal infections, and caution is advised for use in animals with active bacterial infections, corneal ulcers, hyperadrenocorticism (i.e., Cushing’s disease), diabetes mellitus, osteoporosis, chronic psychotic reactions, predisposition to thrombophlebitis, hypertension, and renal insufficiency. In humans, dexamethasone and other corticosteroids have been used in the study and treatment of atopic dermatitis and rheumatoid arthritis.

Dexamethasone has been prescribed to treat a variety of equine conditions, including arthritis, allergic reactions, and heaves. It also provides supportive therapy in a wide variety of cases, such as heat exhaustion, influenza, laminitis, and retained placenta, provided that the primary cause is diagnosed and corrected. It is commonly administered orally (PO), intravenously (IV), or intramuscularly (IM). Dexamethasone and other corticosteroids suppress the body’s natural production of hydrocortisone, a hormone with many important regulatory functions within the body.

Dexamethasone is typically used in the management of various rheumatic, dermatologic, allergic and other diseases known to be responsive to anti-inflammatory corticosteroids. Dexamethasone Solution may be used intravenously as supportive therapy when immediate hormonal response is required.

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 for horses

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

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.