September 2026 Newsletter
The Racehorse Airways: What Happens When a Horse Coughs?
A cough is one of the most common respiratory signs we see in horses, particularly racehorses in training. It can be as simple as a horse clearing a little dust from its airway — but it can also be an early indication of a respiratory infection or inflammation deeper within the lungs.
For a racehorse, maintaining healthy airways is particularly important. During intense exercise, a horse’s respiratory system has to move enormous volumes of air, meaning even relatively mild airway inflammation can potentially affect performance.
So, what actually happens when a horse coughs, and when should we be concerned?
Why does a horse cough?
Coughing is a protective reflex. When the respiratory tract detects something irritating- such as dust, mucus, pollen inflammation or an infectious agent- receptors within the airway trigger a cough.
The aim is simple: remove the irritant from the respiratory tract.
Occasional coughing, particularly when a horse first starts exercising, can therefore be completely benign. However, repeated coughing suggests that something is irritating the respiratory system and deserves further investigation.
Not every cough is an infection
One of the most important things to remember is that a coughing horse does not necessarily have a respiratory infection.
In racehorses, coughing can have several different causes, including:
- Viral or bacterial respiratory infections
- Inflammation of the lower airways
- Dust and environmental irritation
- Allergens such as mould spores
- Accumulation of mucus within the airways
- Exercise-induced airway inflammation
- Less commonly, structural abnormalities of the upper airway
This is why simply treating every cough with antibiotics isn’t necessarily appropriate. Antibiotics do not treat viruses or non-infectious airway inflammation, and unnecessary antibiotic use contributes to antimicrobial resistance.
The importance of the lower airways
The respiratory tract can broadly be divided into the upper and lower airways.
The upper airway includes structures such as the nostrils, nasal passages, pharynx and larynx. The lower airway consists of the trachea, bronchi and the smaller airways leading towards the lungs.
Inflammation in the lower airways can be particularly important in racehorses because it can interfere with the movement of air during exercise.
A horse may appear completely normal at rest but still have significant inflammation within its lower respiratory tract.
This is one reason why a horse that simply has a “little cough” should not necessarily be dismissed, particularly if the cough persists or is associated with a change in performance.
What about mucus?
The respiratory tract naturally produces mucus, which helps trap particles and microorganisms. Normally, this mucus is transported out of the airways by the mucociliary clearance system and swallowed.
When the airways become inflamed, however, mucus production can increase and clearance can become less effective.
This can result in mucus accumulating within the trachea and lower airways.
A horse with significant mucus may cough, particularly during exercise, and may show subtle changes in performance before appearing obviously unwell.
What does this mean for performance?
Racehorses have extremely high respiratory demands during exercise. A thoroughbred galloping at speed can move a huge volume of air through its respiratory tract every minute.
Even relatively mild airway disease can therefore become more apparent during exercise.
Signs that may suggest respiratory disease include:
- Coughing during exercise
- Reduced performance
- Poor recovery after exercise
- Increased respiratory effort
- Nasal discharge
- Increased respiratory noise
- A horse that feels reluctant to gallop
- Repeatedly stopping or losing its finishing effort
Importantly, these signs are not specific to one particular respiratory condition, which is why investigation can be valuable.
When should we investigate a cough?
The context is important.
A single cough at the start of exercise in an otherwise bright horse with no other signs may not be particularly concerning.
However, veterinary investigation is recommended when coughing is:
Persistent — particularly if it continues over several days.
Associated with other signs — such as nasal discharge, fever, lethargy or enlarged lymph nodes.
Repeated during exercise — especially if it is accompanied by a reduction in performance.
Occurring in multiple horses on the yard — this raises the possibility of an infectious respiratory disease and appropriate biosecurity measures should be considered.
Recurrent — repeated episodes of coughing may indicate an underlying airway problem rather than repeated infections.
How do we investigate the respiratory tract?
The first step is usually a thorough clinical examination and discussion of the horse’s history, including when the cough occurs, whether other horses are affected and whether there has been any change in performance.
Depending on the findings, further investigation may include:
Endoscopy
An endoscope allows us to examine the upper airway and, using a longer scope, the trachea.
This can allow us to assess the amount and character of mucus within the airway and identify some upper airway abnormalities.
Tracheal wash
A sample can be collected from the lower respiratory tract and examined for inflammatory cells and other abnormalities.
This can provide useful information about whether inflammation is present and what type of inflammatory response is occurring.
Bronchoalveolar lavage
Bronchoalveolar lavage (BAL) involves collecting a sample from the deeper airways and alveoli.
The sample can be examined cytologically to assess the types and proportions of cells present, helping to identify inflammatory airway disease.
Diagnostic testing for infection
Where an infectious respiratory disease is suspected, appropriate samples may be submitted for laboratory testing.
This can help determine whether an infectious agent is present and can be particularly useful when several horses on a yard are affected.
Don’t forget the environment
The horse’s environment plays a major role in respiratory health.
Dust, mould and poor ventilation can all contribute to airway irritation and inflammation.
Simple management measures can therefore make a significant difference:
- Keep stables well ventilated.
- Minimise dusty bedding.
- Avoid feeding mouldy or dusty forage.
- Consider soaking or steaming hay where appropriate.
- Keep feed and bedding stored away from the stable environment.
- Maximise turnout where practical.
- Avoid sweeping or mucking out around horses wherever possible.
- Ensure good ventilation in transport vehicles.
For horses with recurrent airway inflammation, environmental management is often just as important as any medication prescribed.
What about exercise-induced pulmonary haemorrhage?
Another respiratory condition particularly relevant to racehorses is exercise-induced pulmonary haemorrhage (EIPH) also known as bursting or bleeding.
During intense exercise, the pressures within the pulmonary circulation can become extremely high, and some horses experience bleeding from small blood vessels within the lungs.
Most affected horses do not have an obvious nosebleed. In fact, blood may only be detected by examining the airways after exercise. The significance of EIPH and its management is a complex subject in its own right, but it is an important reminder that respiratory health extends well beyond simply asking whether a horse is coughing
The key message
A cough is a symptom, not a diagnosis.
For some horses it may be nothing more than a brief response to dust or mucus. For others, it can be the first indication of infectious disease or significant airway inflammation.
For the racehorse, where small changes in respiratory function can have a significant impact on performance, persistent or recurrent coughing shouldn’t simply be ignored.
If a horse is coughing repeatedly, particularly if there is a change in performance or other respiratory signs, speak to your veterinary surgeon. Identifying the underlying cause allows treatment and management to be targeted appropriately — rather than simply treating the cough itself.
Healthy airways are essential for a racehorse to perform at its best.
Best wishes,
Patrick