RAO in horses - What equine asthma really is, and how stable management can help

Coughing in horses is often dismissed as minor. Sometimes, it is the first sign of one of the most common chronic diseases.

When a cough is not minor

You often hear it in the stable. A short cough when saddling up. A clearing of the throat when the hay is shaken. "He's always done that, it's nothing serious" – a phrase often heard in many stable aisles.

Sometimes it really is harmless. And sometimes it's the first, quiet hint of one of the most common chronic diseases in horses: RAO – Recurrent Airway Obstruction.

What is RAO – and why is it now called equine asthma?

RAO is a chronic, non-infectious (not caused by bacteria or viruses) inflammation of the lower airways in horses. Previously, the disease was known by various names: COB (Chronic Obstructive Bronchitis), COPD (Chronic Obstructive Pulmonary Disease), or simply "heaves".

Today, veterinary medicine combines all these terms under a new umbrella term: Equine Asthma. This collective term distinguishes two severity levels:

IAD (Inflammatory Airway Disease): the milder to moderate form, which mainly affects younger horses.

RAO (Recurrent Airway Obstruction): the severe form, often referred to as "heaves", which usually occurs in middle-aged and older horses.

The disease shows strikingly many parallels to human asthma – which is why affected horses even serve as a model in research for the study of human COPD diseases.

How common is RAO really?

The numbers are impressive – and should make every horse person sit up and take notice.

Severe equine asthma (the severe form, RAO) is estimated to affect 10 to 15 percent of all horses kept in conventional stables in temperate climates. In older horses, this number increases even further: More than 50 percent of 12- to 14-year-old horses already show signs of chronic obstructive bronchitis.

This means: RAO is not a rare exception. It is one of the most common chronic diseases in the entire horse population.

What happens in the horse's body

To understand why RAO develops, it helps to look at the horse's origins.

Horses, with their large lung volume, are made for outdoor life – for the open steppe, for constant movement, for clean air. Stable housing presents a completely different environment for the sensitive airways than the one they were evolutionarily shaped for.

When a horse susceptible to RAO comes into contact with allergens (substances that trigger an exaggerated immune response) such as dust, mold spores, or pollen, the immune system overreacts. This leads to a massive infiltration of neutrophils (a type of white blood cell that normally fights pathogens) into the airways.

The result is two problems simultaneously: bronchospasm (a painful cramping of the small airways) and increased mucus production. Both together significantly narrow the airways – the horse literally has difficulty breathing.

Two specific triggers have been particularly investigated: Aspergillus fumigatus and Faenia rectivirgula – two types of mold that can occur in hay and straw and have been shown to cause bronchial hypersensitivity.

The most common triggers

The list of triggers is long, but it can be summarized into a few main factors:

Dust from hay and straw – the largest and best-researched source. Every time a horse eats hay or stands in its stall, it inhales millions of particles: dust, mold spores, bacteria.

Ammonia – created during the breakdown of urine and feces. Concentrations as low as approximately 10 ppm (parts per million, a unit of measurement for gas concentration in the air) can irritate the sensitive airway mucous membranes.

Molds from feed – especially with poorly dried or excessively moist stored hay.

Pollen – in a special subtype called SP-RAO (Summer Pasture associated RAO), where symptoms paradoxically occur in the pasture instead of the stable.

Genetic predisposition – some horses are inherently more sensitive than others, even under identical housing conditions.

Recognizing symptoms – from mild cough to heaves

RAO usually develops insidiously, in episodes, with symptom-free periods between episodes. This can make early detection difficult.

Early signs:

• Short cough at the beginning of a training session
• Slightly increased breathing rate after exertion
• Occasional coughing when eating hay

Advanced signs:

• Coughing even at rest, even in the stall
• Nasal discharge
• Flared nostrils
• Increased sweating even with light exertion
• Noticeable performance impairment

Severe signs (Heaves):

• Shortness of breath even when standing
• Visible "heave line" – a line along the abdominal muscles, which results from the increased effort during exhalation
• Significantly reduced performance

Important: A complete cure in the medical sense is often no longer possible in chronic forms – the structural changes in the lungs can be irreversible. This makes early detection even more important.

Diagnosis – how the vet diagnoses RAO

Diagnosis is never made by mere observation alone. A thorough veterinary examination typically includes:

• A comprehensive clinical examination
• Blood gas analysis
• Endoscopy of the airways (an examination with a small camera) followed by taking mucus directly from the trachea for analysis

Stable management – the most important measure of all

Here comes perhaps the most important finding of all RAO research: Treatment does not begin with medication. It begins with the environment.

Wet or steam hay. Simply sprinkling hay with water is not enough – only thoroughly soaked or steamed hay (at least 100°C) is sufficiently dust-free. Important to know: Wet hay increases microorganisms faster, so it should be fed promptly.

Use low-dust bedding. Straw is significantly dustier than finer alternatives. Shavings, pellets, or fine mineral bedding bind moisture better and further reduce dust exposure.

Muck out consistently. Wet spots should be completely removed daily – not just covered. Standing urine is the main source of ammonia formation.

Ensure good ventilation. Even in winter – ammonia is heavier than air and collects at the bottom, where the horse breathes it directly.

Remove the horse from the stable during mucking out and bedding. The greatest dust exposure occurs precisely during these tasks. After about 30 minutes, most of the dust has settled again.

Do not shake or store hay in the stable. Also applies to neighboring stalls: If you have a horse with respiratory problems, you should try to ensure that no additional dust is stirred up in the surrounding area.

Where zeolite and natural support have their place

Important upfront: Zeolite does not cure RAO and does not replace veterinary treatment. The scientifically proven basis of any support remains stable management – working on the causes, not just the symptom.

Where zeolite can usefully supplement, however:

As bedding, finely porous zeolite binds ammonia directly at the source and keeps the stall floor drier – an important component for reducing ammonia exposure in the breathing air.

Fed internally, zeolite can help bind mycotoxins (mold toxins) absorbed through contaminated feed – before they burden the body systemically.

For stable hygiene, a combination of dry, low-ammonia bedding and a stable microbiome through AM+PLUS can help prevent conditions that promote rot and mold in the stable.

We are deliberately cautious here: There are currently no specific, independent studies proving that zeolite directly treats or cures RAO. What it can achieve is to be a useful supplement within a well-thought-out overall concept – alongside hay steaming, good ventilation, and consistent stable management.

FAQ – Frequently Asked Questions

❓ Is RAO curable?
No, not completely in the medical sense – especially if the disease is already advanced and structural changes have occurred in the lungs. However, RAO is reversible in the sense that symptoms can significantly recede or disappear entirely if the triggering factors are consistently removed from the environment.

❓ Can my horse with RAO still be ridden?
In many cases, yes – depending on the severity and veterinary assessment. Individual consultation with the vet is important, as exertion should be avoided during acute episodes.

❓ What kind of bedding is best for RAO?
Low-dust alternatives such as fine shavings, pellets, or finely porous mineral bedding are less dusty than traditional straw and also bind moisture and ammonia better.

❓ Do I have to completely forego hay with RAO?
Not necessarily – but the hay should be consistently soaked or steamed to drastically reduce the dust content. Alternatively, haylage or hay cobs can be a lower-dust option.

❓ How quickly do improvements in stable management take effect?
This varies individually. Some horses show a noticeable improvement after just a few days of consistent dust reduction, while for others – especially in advanced cases – it takes longer or the improvement remains limited.

❓ Can zeolite cure RAO?
No. Zeolite is not a treatment for RAO and should never be understood as a substitute for veterinary care or consistent stable management. As bedding, however, it can contribute to a clear reduction in ammonia exposure. And as a feed additive, zeolite supports the reduction of pollutants and molds.

Read more

👉 HORSEKRAFT Zeolite bedding – against ammonia & thrush →
👉 AM+PLUS for horses – microorganisms for skin & coat →
👉 Zeolite for horses – the big Q&A guide →