Article provided by Equine Guelph**
Equine asthma is one of the most prevalent respiratory conditions affecting horses worldwide, impacting performance, quality of life, and long-term health. While the terminology used to describe this condition may vary between countries—with terms such as Recurrent Airway Obstruction (RAO), Chronic Obstructive Pulmonary Disease (COPD), heaves, or broken wind still commonly used—the underlying condition and its debilitating symptoms remain the same.
This inflammatory airway disease affects horses of all ages, breeds, and disciplines, from leisure horses to elite competition animals. The condition occurs when the airways become hypersensitive to environmental triggers, leading to inflammation, mucus production, and constriction of the small airways in the lungs. Left unmanaged, equine asthma can significantly compromise your horse’s athletic ability, comfort, and overall wellbeing.
The good news is that with proper understanding, environmental management, and appropriate veterinary care, equine asthma can be effectively controlled in most cases. Prevention is always preferable to treatment, and many cases can be avoided or minimised through careful stable management and awareness of environmental risk factors.
In this article, Equine Guelph—a world-leading equine research and education centre—provides expert information on how to recognise, prevent, and manage equine asthma and other related respiratory and breathing issues that our horses can suffer from. Whether you’re concerned about a persistent cough, reduced performance, or simply want to optimise your horse’s respiratory health, this guide will equip you with the knowledge you need to protect your horse’s airways and breathing capacity.
Understanding the triggers, recognising the early warning signs, and implementing effective management strategies can make the difference between a horse that struggles with chronic respiratory problems and one that breathes freely and performs to their full potential.
Have you ever walked into a stable, and felt like your lungs were being assaulted? This is how a horse feels, particularly if they spend hours in a stable. When horses exercise, they take on upwards of 16 times as much air per second than their human owners. Their lung capacity is enormous, as are their athletic capabilities unless they are compromised by environmental factors. Much can be done from a management standpoint to minimize dust and harmful particulates in a horse’s environment while maximizing athletic function and general comfort in the process.
When horses exercise, they take on upwards of 16 times as much air per second than their human owners.
Even a horse not exhibiting signs of breathing issues may be under assault from airborne particles. Every effort should be taken to minimize dust to practice prevention of irreversible breathing issues.
The culprits we can control
- Keep hay and bedding fresh, as these are two of the top sources of mould and particulate in a horse’s environment
- Consider wetting or steaming hay prior to feeding or hay alternatives if the horse is triggered by the hay in its diet. Research has been conducted on steamed hay vs soaked and the variable nutrient losses to consider, so be sure to discuss this option with your vet and nutritionist.
- Consider highly absorbent shavings over straw
- Ventilation is a primary concern when building a barn but many stables are lacking. Ensure you have good airflow through your stable and periodically remove the cobwebs as you clean your barn.
- Horses take in 64-70 litres of air per second when exercising. Footing in the arena needs to be regularly maintained to keep dust from rising into the air.
- Do not sweep dust and debris from the barn aisle into your horse’s stable, in fact, don’t sweep at all when horses are in the barn if possible
- Dappen down the floor before you begin and wear a mask for your own respiratory health
- Keep horses outside as much as possible, unless medical conditions require stalling.
Have a look below at Equine Guelph’s Defend Against Dust fact sheet and infographic shared by Equine Guelph sponsor, Boehringer Ingelheim.
Signs and Symptoms of Equine Asthma
Recognising the signs of equine asthma early is crucial for effective management and preventing the condition from progressing to a more severe, chronic state. The symptoms can range from subtle changes that are easily overlooked to obvious respiratory distress that significantly impacts your horse’s quality of life and performance. Understanding what to look for enables you to intervene quickly and work with your veterinary surgeon to implement an appropriate treatment and management plan.
Key Clinical Signs of Equine Asthma
Coughing
A persistent cough is often the first and most noticeable sign of equine asthma. This may present as occasional coughing when the horse first starts exercise, a chronic cough throughout the day, or coughing fits triggered by dust, feeding, or changes in environment. The cough occurs as the horse attempts to clear mucus and debris from inflamed, narrowed airways. Some horses cough more frequently when stabled or when hay is shaken out, whilst others may cough primarily during the first few minutes of work as they begin to breathe more deeply. A cough that persists for more than a few days, worsens over time, or is accompanied by other respiratory signs warrants veterinary investigation.
Nasal Discharge from Mucus Production
Increased mucus production is a hallmark of equine asthma, as the inflamed airways produce excessive secretions in response to irritation. You may notice nasal discharge ranging from clear and watery to thick, white, or occasionally yellow mucus. The discharge is typically bilateral (from both nostrils) and may be more noticeable after exercise or coughing episodes when mucus is expelled from the lower airways. While a small amount of clear discharge can be normal, persistent or copious nasal secretions—particularly if thick or discoloured—indicate significant airway inflammation and mucus accumulation in the lungs.
Exercise Intolerance
Horses with equine asthma often show a marked decline in athletic performance and stamina. This exercise intolerance occurs because the narrowed, inflamed airways cannot deliver sufficient oxygen to meet the demands of physical exertion. You may notice your horse tiring more quickly than usual, showing reluctance to work, taking longer to recover after exercise, or displaying reduced enthusiasm for activities they previously enjoyed. Performance horses may struggle to maintain their usual level of work, show slower times, or refuse jumps. In severe cases, even light exercise such as walking or trotting may cause laboured breathing and distress. This progressive loss of performance is often gradual, making it easy to attribute to other factors such as fitness, age, or lack of motivation, which is why awareness of other concurrent symptoms is so important.
Difficulty Expelling Air
One of the characteristic features of equine asthma is difficulty with expiration—breathing out. While healthy horses breathe in and out in a smooth, effortless motion, horses with asthma must work harder to push air out of their constricted airways. You may observe increased abdominal effort during breathing, where the horse uses their abdominal muscles to forcefully expel air from the lungs. This creates a distinctive two-phase expiratory effort, where you can see the abdomen lift in two distinct movements rather than one smooth motion. The horse may also have an increased respiratory rate at rest, flared nostrils, or appear to be breathing with visible effort even when not exercising.
Heave Line
In chronic, severe cases of equine asthma, a visible “heave line” may develop along the horse’s abdomen. This is a ridge of hypertrophied (enlarged) muscle that runs along the lower edge of the ribcage, created by the constant, excessive use of abdominal muscles to force air out of the lungs. The heave line appears as a distinct groove or line of muscle definition and indicates long-term, significant respiratory compromise. The presence of a heave line suggests the condition has been present for an extended period and that the horse has been working very hard to breathe. While this sign indicates advanced disease, it’s important to note that horses can have significant equine asthma without developing a heave line, particularly if the condition is identified and managed before it reaches this chronic stage.
Inflammation of Lung Epithelium and Narrowing of the Bronchi
The underlying pathology of equine asthma involves inflammation of the epithelial lining of the airways and constriction (narrowing) of the bronchi and bronchioles—the small airways in the lungs. This inflammation causes the airway walls to thicken, reduces the diameter of the air passages, and triggers excessive mucus production, all of which impair airflow and gas exchange. While you cannot directly observe this internal inflammation, your veterinary surgeon can confirm it through diagnostic procedures.
Bronchoalveolar Lavage (BAL) is the gold standard diagnostic test for equine asthma. This procedure involves passing an endoscope (a flexible camera) through the horse’s nostril, down the trachea, and into the lungs. Sterile saline solution is then flushed into a section of the lung and immediately suctioned back out, collecting cells and mucus from the small airways. The fluid is analysed in a laboratory to identify the types and numbers of inflammatory cells present—particularly neutrophils, which are elevated in horses with equine asthma. A BAL provides definitive diagnosis, helps determine the severity of the condition, and can guide treatment decisions. It also helps rule out other respiratory conditions such as infectious diseases or exercise-induced pulmonary haemorrhage.
Additional Signs to Monitor
Beyond the primary symptoms, horses with equine asthma may also display:
- Reduced appetite due to difficulty breathing while eating
- Weight loss from increased energy expenditure of laboured breathing
- Nostril flaring at rest or with minimal exertion
- Increased respiratory rate (normal is 8-16 breaths per minute at rest)
- Abnormal lung sounds such as wheezes or crackles (detected by your vet with a stethoscope)
- Reluctance to lie down as this can worsen breathing difficulty
- Anxiety or restlessness associated with respiratory discomfort
When to Call Your Vet
If your horse displays any combination of these signs—particularly a persistent cough, nasal discharge, and reduced performance—contact your veterinary surgeon promptly. Early intervention can prevent progression to chronic, irreversible airway damage and significantly improve your horse’s prognosis and quality of life. Your vet can perform a thorough respiratory examination, including listening to lung sounds, assessing breathing effort, and potentially performing diagnostic procedures such as endoscopy or BAL to confirm the diagnosis and determine the most appropriate treatment and management strategy.
Remember that equine asthma is a manageable condition when identified early and addressed with appropriate environmental modifications and veterinary care.
Dr. Dorothee Bienzle illustrates signs of heaves/asthma in this video.
Why Practice Diligent Prevention?
Irreversible damage can be done by the cumulative effect from years of exposure to dust, mould and other particulate matter.
If a horse is coughing and asthma is suspected, the veterinarian will be looking closely at the horse’s environment to determine what is causing the irritation in the lungs. They will be looking at all potential causes which could include: dusty environments, smoke inhalation, pollen or other allergens and particles in the pasture or hay.
Don’t wait for your horse to start coughing to practice prevention. If your horse begins to cough, call the vet right away to investigate the cause. When dealing with respiratory ailments early diagnostics, aggressive treatment and environmental management are of paramount importance.