Equine Asthma in Horses

What equine asthma is, the signs to watch for, how a vet confirms it and how everyday management helps keep it under control.

Quick Answer

Equine asthma is an inflammatory airway condition, usually linked to dust, mould and other particles in the air, and it is not contagious to other horses.
It comes in two forms, mild-to-moderate and severe, and coughing, nasal discharge and tiring easily are common signs.
Other respiratory illnesses look similar, so your vet needs to confirm the cause before treatment starts.
Managing the environment is the most important part of control, because medicine alone is not enough.
If your horse is struggling to breathe while resting or seems distressed, phone your vet straight away.

Equine asthma is a long-term inflammatory condition of the lower airways. It is the umbrella name vets now use for what used to be called heaves, recurrent airway obstruction (RAO), COPD or inflammatory airway disease.

In most cases it is linked to the air your horse breathes, so daily management matters as much as medicine. This guide explains the signs, how a vet confirms the diagnosis and what you can change at home. For other reasons a horse may cough, see Why Is My Horse Coughing?

Close-up of a chestnut horse's muzzle in a bright stable – equine asthma can show as coughing, nasal discharge or tiring easily

What causes equine asthma?

Equine asthma is not an infection. UK sources describe it as non-infectious and not contagious, and most cases are linked to the environment.

An allergic-type reaction in the airways

Susceptible horses react to tiny particles they breathe in. The British Horse Society (BHS) compares this to an allergic reaction in people.

The small airways become inflamed and the lining thickens. Extra mucus builds up, so the horse has to work harder to breathe.

Dust, mould and gases in the stable

Airborne particles small enough to enter the airways are called aeroallergens. They include dust, mould, bacteria, mites, plant debris and pollen. Toxic gases such as ammonia can also act as triggers.

Blue Cross says that in most cases the triggers are found in the stable or hay. Poor bedding choices or too little ventilation can raise the level of these particles.

If you can smell ammonia in the stable, it is likely to be irritating the airways already.

Pollen and pasture

Some horses get worse at grass rather than in the stable. One type, summer pasture-associated severe equine asthma (SPASEA), is seen in horses kept at pasture and is triggered by pollen. It is described as particularly prominent in summer.

Timing varies from horse to horse and between types. Blue Cross says equine asthma is often worse in summer but can cause problems all year round, while VetPartners says stabled horses are most affected in winter and spring. So avoid assuming it only happens in one season.

White horse looking out of a stable window – good ventilation is an important part of managing equine asthma

Other factors that may play a part

Mild-to-moderate disease is more often seen in younger horses. Severe disease frequently affects older horses.

A UK vet article reports earlier research finding a five times greater incidence of severe equine asthma in the offspring of affected horses than in the offspring of unaffected parents. The article says this suggests genetics may play a part.

Blue Cross also says asthma can develop after other respiratory illnesses, such as strangles or flu.

Signs of equine asthma to look for

Most horses show one or more of these signs. The BHS and Blue Cross lists overlap closely.

Coughing, which may be occasional rather than constant
Nasal discharge, from clear mucus to thick green or yellow
Tiring easily, poor performance or reluctance to exercise
Slow recovery after exercise, or a faster breathing rate
Nasal flaring or noisy breathing (wheezing)
Weight or appetite loss in some severe, long-standing cases

Mild-to-moderate disease typically shows no signs at rest. A UK vet article describes the milder form as often showing up as poor performance or a chronic cough lasting more than three weeks. You do not need to wait that long to ask your vet to check.

Severe asthma is different. These horses make an obvious effort to breathe even while resting. You may also see a heave line, a visible line just behind the rib cage caused by enlarged abdominal muscles working to push air out.

Coughing is not a reliable marker on its own. The Royal Veterinary College (RVC) notes that a significant proportion of horses with respiratory disease do not cough, or cough only occasionally.

Emergency: Contact a Vet Immediately If…

Your horse is struggling to breathe while standing still, or is breathing hard with flared nostrils.
Your horse seems distressed or cannot settle because of its breathing.
Breathing suddenly becomes much worse after heavy exposure to dust or pollen.

Call your vet or the nearest out-of-hours emergency vet straight away.

When to Contact Your Vet

Your horse shows any signs of asthma, such as coughing, nasal discharge or tiring easily.
A cough keeps going (a UK vet article calls a cough of more than three weeks chronic), or your horse's performance has dropped.
Your horse has a temperature above 38.5°C, swollen glands, a thick pus-like discharge, or is off colour or off its food. These point towards infection rather than simple asthma.
Signs come back or worsen after an improvement.

Do not assume every cough is asthma. Infections such as strangles and equine flu can look similar early on.

How vets confirm equine asthma

The first examination

Your vet will do a full clinical examination and ask about your horse's management and any exposure to dust, pollen or fungal spores. This history often gives the first clue.

Early respiratory signs look alike, so laboratory tests are frequently needed. For poor performance, the vet may also rule out other causes such as upper airway, heart or musculoskeletal problems.

Looking inside the airways

Endoscopy is the tool vets use most. A camera on a long flexible tube is passed through the nose into the windpipe, usually with the horse sedated. A large build-up of mucus may be visible.

Vets may also take a washing from the lower airways, called a bronchoalveolar lavage (BAL). Examining those cells helps confirm asthma and separate the mild-to-moderate form from the severe form. In the same vet article, some blood markers studied in mild cases did not match the lavage results.

Ruling out infection first

Treatment often involves anti-inflammatory medicines, so vets exclude an active infection beforehand. Swabs can screen for viruses such as flu and equine herpesvirus.

Managing equine asthma day to day

Vets and welfare charities agree that environmental management is the most important part of control. Medicine eases the signs, but they return if the horse stays in an allergen-rich environment.

Stable, bedding and ventilation

Use low-dust bedding, such as dust-extracted shavings, paper, cardboard or pelleted straw.
Muck out daily. Deep-litter bedding is the least suitable for respiratory health.
Keep air moving through doors, vents and windows, and make sure flooring drains.
Take your horse out while you muck out or sweep, as dust can hang in the air for around 30 minutes.
Groom in an open, airy space and sweep the yard daily.

Latex and dust in some arena surfaces can also irritate the airways, so outdoor exercise is recommended where possible.

Forage and feeding

Feed is the largest source of dust that horses breathe in. Soaking hay by fully immersing it, steaming it, or feeding good-quality haylage can all reduce the dust. Hosing hay down is often not enough.

Feeding from the ground encourages the head to lower and the airways to clear. Always check forage for visible white or brown mould, and keep hay and bedding stored dry and away from the stable.

These steps do not suit every horse, so ask your vet if signs continue.

Turnout and pollen

More turnout is one of the best ways to cut dust exposure. However, horses sensitive to pollen can get worse at pasture. Do not turn out every asthmatic horse as a rule. Follow your vet's advice for your horse.

Medicines your vet may prescribe

Your vet may prescribe medicines to reduce airway inflammation and, in more severe cases, to help open the airways. How they are given depends on how severe the condition is, and your vet decides.

Relying on medicine without improving the environment can be detrimental, because the horse may breathe more allergens deeper into the lungs.

In the UK, horses are food-producing animals. The passport declaration decides which medicines can be given and what records must be kept, so mention the passport to your vet. If you compete, ask your vet and check your sport's rules.

How Pet Med Direct Can Help

Your vet should be your first call for any breathing problem. Pet Med Direct supplies horse care products, which you can browse in our equine range.

If your vet has prescribed a medicine, prescription-only medicines (POM-V) are supplied solely against a valid prescription from the horse's own vet. You can read how pet prescriptions work before you order.

Some pet medicines require a valid veterinary prescription. Pet Med Direct can only supply prescription medicines after the prescription has been checked. Always follow your vet's advice and the directions on the medicine label.

Frequently Asked Questions

Is asthma in horses contagious?

No. UK sources describe it as non-infectious and not contagious to other horses. However, a horse with a cough or discharge could have an infectious illness instead, so it is worth asking your vet to check.

Is it the same as heaves or COPD?

They are older names for the same family of conditions. The name equine asthma now covers heaves, RAO and inflammatory airway disease. The term COPD was dropped because the disease process differs from human COPD.

Does asthma in a horse go away?

UK sources talk about managing it. The RVC says most younger horses with the milder inflammatory airway disease appear to recover, but the severe form (RAO) tends to be persistent, so permanent environment changes are usually needed.

Does asthma cause a fever?

Not usually. A raised temperature is rare unless a secondary infection is involved. A fever above 38.5°C, swollen glands or loss of appetite point towards infection, so call your vet.

Can a horse with asthma still be ridden or compete?

A UK vet fact sheet says affected horses can be managed for both pleasure riding and competition. Success depends on dedicated owners and good management. Your vet can advise on what suits your horse.

How long should I soak hay?

The BHS says to fully immerse hay for no more than 30 minutes, to avoid losing too many nutrients. Steaming keeps more nutrients and helps kill mould and bacteria, but home-made steamers that do not reach temperature can increase them. Ask your vet if you are unsure.

Is dusty hay the only trigger?

No. Mould, mites, bacteria, pollen and gases such as ammonia can all act as triggers. That is why bedding, ventilation, mucking out and turnout all matter alongside forage.

Related Equine Health Guides

Sources and Further Reading

This article was researched from the sources listed above. It is general information for horse owners and is not a substitute for advice from your own vet.

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This article is for informational purposes only and does not constitute veterinary advice.
If you are concerned about your horse’s health, please consult a qualified veterinarian.