Heaves in Horses: Severe Equine Asthma Signs and Management
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By Dr Duncan Houston
A horse using its belly to push air out is working harder to breathe than it should. A recurring cough may be an earlier clue, but obvious effort at rest needs prompt attention.
Heaves is now usually described as severe equine asthma. Medication can help, but lasting control depends heavily on what the horse breathes every day.
Quick Answer
Severe equine asthma causes airway inflammation, narrowing and mucus that can produce cough, exercise intolerance and laboured breathing at rest. Stop exercise and call your vet if breathing becomes difficult. Reduce relevant dust or pasture triggers and follow an individual medication plan; antibiotics are not routine treatment for asthma itself.
What is happening in the airways?
Inflamed, narrowed airways make it harder to move air, especially during expiration. Repeated effort can produce a visible abdominal “heave line”, but that line is not required for diagnosis.
The Merck equine asthma reference distinguishes mild to moderate asthma from the severe disease previously called recurrent airway obstruction. Younger horses with cough or poor performance may have a different severity pattern from an older horse struggling at rest.
Dust, mould and other airborne material from forage and bedding are common contributors. Some horses worsen on pasture in particular seasons, so “more turnout” is not a universal prescription.
How urgent are the signs?
| Finding | Action |
|---|---|
| Recurring cough or unexplained reduced performance | Arrange examination and review air quality. |
| Flared nostrils or obvious abdominal breathing at rest | Contact your vet promptly and stop exercise. |
| Severe distress, weakness, collapse or rapidly worsening breathing | Emergency veterinary care. |
Could this be infection or another disease?
Pneumonia, upper-airway obstruction, heart disease and other respiratory disorders can cause similar signs. Fever, marked dullness or sudden onset changes the investigation. Asthma is not contagious, but an undiagnosed cough should not automatically be labelled asthma.
Your vet listens to the chest and may recommend endoscopy, airway sampling or imaging. The ACVIM consensus on inflammatory airway disease emphasises documenting airway disease and excluding alternatives. A severely breathless horse is stabilised before stressful testing.
When is this an emergency?
Call immediately if your horse is struggling to breathe, becomes weak or deteriorates rapidly. Keep it quiet in the cleanest accessible air and avoid unnecessary movement. Do not exercise it to clear mucus, place a bag over its nose or attempt a home rebreathing test.
What should you do next?
- Stop work and contact your vet with cough history, breathing changes and environmental triggers.
- Move away from active dust if this can be done without distress.
- Review forage, bedding, ventilation, sweeping and nearby hay storage.
- Follow the prescribed medication and administration instructions.
- Track resting breathing effort, cough, appetite and response after each management change.
Dust exposure occurs close to the nose, so simply opening a stable door may be insufficient. Avoid mucking out, sweeping or shaking hay near the horse. Low-dust bedding and a suitable forage strategy need to work throughout the building, not only in one box.
What about hay and turnout?
Steaming, soaking or replacing forage with an appropriate lower-dust ration may help selected horses, but nutritional balance, handling and spoilage need attention. Do not remove necessary fibre without a replacement plan.
The MSD owner guidance notes that pasture-associated cases may need pasture avoidance. Identify the individual trigger pattern rather than assuming every horse improves outdoors.
How does medication help?
Corticosteroids reduce inflammation, while bronchodilators relieve airway narrowing. The route and combination depend on severity and the horse’s health. Inhaled medication can target the airways, but it is not automatically suitable or risk-free in every case.
Tell the vet about metabolic disease or previous laminitis. Do not copy another horse’s prescription or stop and restart drugs without a plan. Environmental improvement remains necessary even when medication quickly makes breathing look easier.
Common mistakes
- Accepting a chronic cough as normal.
- Relying on medication while continuing dusty feeding.
- Assuming turnout helps every asthma phenotype.
- Exercising a horse with increased effort at rest.
- Using antibiotics without evidence of bacterial infection.
Preventing flare-ups
Maintain the effective environment consistently, including during travel and seasonal changes. Keep written instructions for carers and review control before increasing work. Appropriate exercise can be useful when breathing is stable, but veterinary clearance should guide the return.
Frequently asked questions
Is heaves curable?
It is usually a long-term condition, but many horses achieve useful control and comfortable periods.
Can my horse still be ridden?
Possibly when stable and assessed as fit for the planned work.
Is it contagious?
Asthma itself is not, although other causes of cough can be.
Are inhalers always better?
No. Severity, delivery, cost and individual risks determine the best treatment plan.
Good control combines easier breathing today with fewer triggers tomorrow. Both deserve attention.
For help understanding your horse’s care and preparing questions for your veterinarian, visit ASK A VET™. Urgent signs need an equine veterinarian in person.
