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 for Horses

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.

Dexamethasone Adverse Effects and Warnings

Adverse effects connected with dexamethasone can include dull/dry coat, increased appetite, weight gain, panting, vomiting, diarrhea, elevated liver enzymes, GI ulceration/perforation (especially with high parenteral or oral doses), hypercoagulability, hyperlipidemia, activation or worsening of diabetes mellitus, muscle wasting, and behavior changes (eg, depression, lethargy, aggression).⁵ Glucocorticoids have been known to delay growth in young animals.⁴

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

Dexamethasone Dosages for Horses

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

Dexamethasone dosage for horses with heaves and dexamethasone for horses with COPD (Adapted from Plumb’s Veterinary Drugs):

Anti-inflammatory; glucocorticoid agent (Labeled dosage): Dexamethasone 2.5 – 5 mg (total dose) IV or IM; dexamethasone sodium phosphate: 2.5 – 5 mg (total dose) IV. 

Adjunctive treatment of recurrent airway obstruction (extra-label): 

a) For a 500-kg horse, dexamethasone 40 mg (total dose; NOT mg/kg) IM once every other day for 3 treatments, followed by 35 mg (total dose; NOT mg/kg) IM once every other day for 3 treatments, followed by 30 mg (total dose; NOT mg/kg) IM once every other day for 3 treatments; continue tapering until horse is weaned off this therapy.

b) For short-term treatment with environmental control: dexamethasone sodium phosphate dosed at 0.1 mg/kg IM once daily for 4 days, 0.075 mg/kg IM once daily for 4 days, and 0.05 mg/kg IM for 4 days. Except for bronchoalveolar lavage cytology results, PO prednisolone (1 mg/kg PO for 4 days, 0.75 mg/kg PO for 4 days, 0.5 mg/kg PO for 4 days) was shown to be as effective as IM dexamethasone.

c) Dexamethasone 0.05 mg/kg IM every 24 hours is as effective as inhaled fluticasone in reducing clinical signs, airway inflammatory cells, and bronchoprovocative histamine response.

d) Dexamethasone at 0.05 mg/kg PO once daily for 7 days or prednisolone at 2 mg/kg PO once daily for 7 days. Both are effective, but dexamethasone proved more efficacious.

Dexamethasone suppression test to diagnose pituitary pars intermedia dysfunction (extra-label): 

a) 20 mg (total dose; NOT mg/kg) IM. Normal values: Cortisol levels should decrease by 50% in 2 hours, 70% in 4 hours, and 80% in 6 hours. At 24 hours, cortisol levels should remain depressed by ≈30% of presuppression value.44 Seasonal variability may effect results.

b) After baseline cortisol (serum or plasma) is collected, dexamethasone 0.04 mg/kg IM can be administered and a second cortisol sample collected 18 to 20 hours later. Cortisol values greater than 10 μg/mL are diagnostic. Testing performed in autumn is more likely to yield false-positive results.

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 10 MG/SCOOP, ORAL POWDER, 100 SCOOPS (5CC SCOOP) by NexGen Pharmaceuticals is indicated for the treatment of acute musculoskeletal inflammations, such as bursitis, osselets, carpitis, myositis, tendonitis and sprains. If bony changes do exist in any of these conditions, joints or accessory structures, responses to dexamethasone cannot be expected.⁴

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.

⁴Plumb’s Veterinary Drugs.

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