Heaves — now more accurately termed severe equine asthma or recurrent airway obstruction (RAO) — is a chronic inflammatory respiratory condition affecting mature horses, analogous to human asthma. It is part of a spectrum of equine asthma syndrome that includes inflammatory airway disease (IAD, the milder form) and severe equine asthma (heaves/RAO). The condition is triggered by inhalation of organic dust, mold spores, and other airborne allergens, primarily from hay and stall bedding. Environmental management is the cornerstone of treatment, and without it, pharmacological therapy alone is insufficient.

Overview

In equine asthma, inhaled allergens and irritants trigger an exaggerated immune response in the airways, leading to bronchoconstriction (airway narrowing), mucus overproduction, and neutrophilic inflammation. Over time, chronic inflammation leads to airway remodeling — thickening of the airway walls and smooth muscle hypertrophy — that may become partially irreversible.

The spectrum ranges from mild (IAD: subtle performance limitation, intermittent cough, increased tracheal mucus) to severe (heaves/RAO: labored breathing at rest, marked expiratory effort with a visible “heave line” along the abdomen). A related condition, summer pasture-associated obstructive pulmonary disease (SPAOPD), occurs in horses pastured in warm, humid climates and is triggered by outdoor allergens.

Causes & Risk Factors

  • Organic dust exposure — Hay dust, mold spores (Aspergillus, Faenia rectivirgula), endotoxins, and inorganic particulates are the primary triggers
  • Stabling — Horses kept in barns with poor ventilation and dusty hay/bedding are at highest risk
  • Age — Severe equine asthma (heaves) typically develops in horses over 7-9 years old; IAD can affect younger horses
  • Genetic predisposition — Some familial tendency has been identified
  • Round bales and poor-quality hay — Higher mold and dust content
  • Bedding type — Straw bedding is particularly dusty; some shavings can also be problematic
  • Indoor arena work — Dusty footing materials can exacerbate respiratory disease

Symptoms

Inflammatory Airway Disease (Mild-Moderate Equine Asthma)

  • Intermittent cough, especially during exercise or feeding
  • Exercise intolerance or poor performance
  • Increased mucus in the trachea (visible on endoscopy)
  • Normal breathing at rest

Heaves / RAO (Severe Equine Asthma)

  • Chronic cough (may be dry or productive)
  • Increased respiratory effort at rest, especially on expiration
  • Flared nostrils
  • “Heave line” — a visible hypertrophied line of abdominal muscles along the lower chest wall from chronic forced expiration
  • Nasal discharge (often bilateral, mucoid to mucopurulent)
  • Exercise intolerance progressing to difficulty breathing at rest in advanced cases
  • Wheezes and crackles on lung auscultation
  • Weight loss in severe chronic cases

Diagnosis

  • Clinical examination — Observation of respiratory rate, effort, and pattern; auscultation of lungs; identification of heave line
  • Rebreathing bag examination — A plastic bag held over the nostrils briefly forces deeper breathing, accentuating abnormal lung sounds
  • Endoscopy — Tracheal examination reveals excess mucus accumulation; bronchoalveolar lavage (BAL) is the key diagnostic test
  • Bronchoalveolar lavage (BAL) — Fluid samples from the lower airways are analyzed for cell populations. Neutrophilia greater than 25% on BAL cytology is diagnostic for severe equine asthma; IAD may show increased neutrophils, eosinophils, or mast cells
  • Thoracic radiographs or ultrasound — May show bronchial thickening and interstitial patterns in advanced cases
  • Pulmonary function testing — Available at referral hospitals; demonstrates increased airway resistance and decreased lung compliance

Treatment & Medications

Environmental Management (Most Important)

  • Maximum turnout — Keeping the horse outdoors 24/7 is the single most effective intervention. Even a few hours of stabling can trigger airway inflammation.
  • Hay alternatives — Soaking hay (30-60 minutes), steaming hay (commercial hay steamers reduce respirable particles by 98%), or replacing hay with haylage, hay cubes, or complete pelleted feeds
  • Bedding — Low-dust options such as cardboard, paper, or dust-extracted shavings. Avoid straw.
  • Ventilation — If stabling is necessary, maximize airflow (open doors, windows, ridge vents)
  • Barn management — Do not sweep aisles while the horse is in the barn, store hay and straw away from the horse’s airspace, and feed from ground level

Pharmacological Treatment

  • Clenbuterol (Ventipulmin) — An oral beta-2 agonist bronchodilator. FDA-approved for horses. Relaxes airway smooth muscle and improves mucociliary clearance. Used for acute exacerbations and short-term management. Not a substitute for environmental control.
  • Dexamethasone — A potent systemic corticosteroid used to rapidly reduce airway inflammation during acute flare-ups. Typically given IV or IM initially, then transitioned to oral prednisolone for tapering. Long-term systemic corticosteroid use carries risk of laminitis, immunosuppression, and other side effects.
  • Inhaled corticosteroids (fluticasone, beclomethasone, ciclesonide) — Delivered via an equine-specific mask and spacer (e.g., Aerohippus, Equine Haler). Target medication directly to the lungs with minimal systemic effects. Fluticasone is the most commonly used. Preferred for long-term maintenance in horses that cannot be maintained on environmental management alone.
  • Ipratropium bromide (inhaled) — An anticholinergic bronchodilator delivered by inhalation. Provides rapid bronchodilation with fewer systemic effects than clenbuterol.
  • Prednisolone (oral) — Used for tapering after dexamethasone or as lower-potency maintenance. Carries some risk of laminitis with prolonged use.

Prognosis

  • With rigorous environmental management, many horses with equine asthma can be well controlled and return to athletic function
  • IAD in young horses often resolves or improves significantly with environmental changes
  • Severe equine asthma (heaves) is a chronic, relapsing condition that requires lifelong management
  • Horses with established heave lines and long-standing disease may have irreversible airway remodeling, limiting the degree of improvement achievable
  • Prognosis is directly tied to the owner’s ability to minimize dust and allergen exposure
  • Failure to address environmental triggers renders pharmacological therapy largely ineffective

Frequently Asked Questions

Is equine asthma the same as heaves? Yes. “Heaves” is the traditional term for what is now classified as severe equine asthma or recurrent airway obstruction (RAO). The terminology was updated to reflect the disease spectrum from mild (IAD) to severe (heaves/RAO).

Can my horse live outside year-round to manage heaves? For many horses with equine asthma, 24/7 turnout with shelter is the ideal management. Horses are well adapted to outdoor living with appropriate shelter, rugs, and access to low-dust feed. Discuss logistics with your veterinarian.

Is soaking hay enough? Soaking reduces respirable dust particles significantly but does not eliminate mold spores as effectively as commercial hay steaming. For severely affected horses, steamed hay, haylage, or complete pelleted feed may be necessary.

Will my horse need medication forever? Some horses can be managed with environmental changes alone after initial pharmacological stabilization. Others require intermittent or ongoing inhaled corticosteroids, especially during seasonal flare-ups or when complete environmental control is not possible.

This information is for educational purposes only and does not replace professional veterinary advice. Consult your equine veterinarian for diagnosis and management of respiratory disease in your horse.