Equine asthma is a common inflammatory disease of the lower airways. It ranges from mild disease, where the only signs may be an occasional cough or reduced performance, to severe disease with persistent coughing and increased effort to breathe at rest.

The terminology has changed over time. Conditions previously described as inflammatory airway disease (IAD) and recurrent airway obstruction (RAO, or “heaves”) are now generally considered part of the equine asthma spectrum. Importantly, mild and severe asthma are not necessarily progressive stages of the same disease.

What Does Equine Asthma Look Like?
Clinical signs depend on the severity of disease.

Horses with mild-to-moderate asthma may have an intermittent or chronic cough, reduced performance or exercise intolerance, increased mucus in the airways, and will often have few or no obvious abnormalities while at rest.

Horses with severe asthma may have frequent coughing, exercise intolerance, and increased respiratory effort even at rest.

Buttermilk's Case
Buttermilk is a 17yr old Haflinger gelding that was presented to Woodside Equine Clinic on emergency for having increased periods of laying down and overall not acting like his usual self. On his physical exam, the only abnormality to note was an increased respiratory rate and mild increased respiratory effort. Upon further investigation, it was noted that Buttermilk has had an increased respiratory rate compared to the other horses and an occasional cough since he arrived. He had been treated with oral antihistamines for presumed allergies which seemed to help, but not resolve the issue. At that time, equine asthma became a topic of conversation.

How Is Equine Asthma Diagnosed?
Diagnosis starts with the history and physical examination. The veterinarian will consider the horse's cough, performance, environment, seasonality, and other possible causes of respiratory or performance problems.

Additional testing may include:
Airway endoscopy: An endoscope allows the veterinarian to evaluate the airways and assess the amount of mucus present. The presence, quantity, and quality of mucous reflects the severity and nature of airway inflammation.

Bronchoalveolar lavage (BAL): A small sample of fluid is instilled into the lower airway and then collected and evaluated for inflammatory cells. This can help document and differentiate the type of lower-airway inflammation, particularly in horses with subtle clinical signs.

Clinical Pathology: Bloodwork can help differentiate clinical signs of equine asthma from those of other lower airway diseases such as bronchopneumonia.

Imaging: Thoracic ultrasound and thoracic radiographs are additional diagnostic tools that can be used to support a diagnosis of equine asthma or help differentiate from other lower airway diseases or conditions.

Buttermilk's Case
In Buttermilk's case, diagnostic testing was important because his clinical presentation alone did not tell the whole story. While the physical exam was helpful, we still needed more information. On initial presentation, blood was collected to assess his blood counts, inflammatory markers, and to look for other signs of inflammation or infection. When bloodwork helped rule out other causes of lower airway disease, Buttermilk’s owner elected to proceed with a Bronchoalveolar Lavage (BAL). This was performed in the field on a different day and the fluid collected was sent to a laboratory for analysis.

Buttermilk’s report came back as moderate-severe mast cell-mediated inflammation, consistent with mast cell phenotype equine asthma.

How Is Equine Asthma Treated?
Treatment has two main components: environmental management and medication when indicated.

Environmental Management
Reducing exposure to airborne particles is a key part of managing equine asthma. This may include:
Improving barn ventilation.

• Reducing dust from hay and bedding
• Using lower-dust feed and bedding options
• Considering alternative methods of hay preparation or feeding
• Maximizing turnout when appropriate
  
  Environmental management is not simply an additional step, it addresses an important source of airway irritation and is a crucial part of asthma management.

Medications
When medication is needed, there are several options, and the best choice depends on the individual horse and severity of disease.

Oral medications can be used to deliver anti-inflammatory medications such as corticosteroids or bronchodilators. Oral therapy can be practical for some horses, although systemic medications can have more effects throughout the body.

Nebulized or inhaled medications, like corticosteroids or bronchodilators, deliver medication directly to the respiratory tract. Inhaled corticosteroids are commonly used, and aerosol therapy may reduce systemic exposure compared with systemic corticosteroids. Medication can be delivered using an equine-specific inhaler or nebulizer, depending on the medication and treatment plan.

The choice between oral, inhaled/nebulized, or combination therapy should be individualized based on the horse's clinical signs, diagnostic findings, response to treatment, and practical considerations for the owner.

Buttermilk's Case
Buttermilk's treatment plan combined management of his environment with medical therapy appropriate for his disease. Following treatment, Buttermilk’s respiratory rate and effort returned to normal and his overall attitude brightened.

His case highlights an important point: managing equine asthma is not just about treating a cough. The goal is to control airway inflammation and improve respiratory function and performance.

Take-Home Points
Equine asthma can be subtle. A horse does not need to be visibly struggling to breathe to have significant lower-airway disease.

If a horse has a persistent cough, unexplained decline in performance, or other respiratory changes, it is worth discussing with your veterinarian. Appropriate diagnostics can help determine whether asthma is present and distinguish it from other causes of respiratory or performance problems.

For horses diagnosed with asthma, environmental management is a cornerstone of treatment, with medications added when appropriate.

Buttermilk's case is a useful reminder that recognizing the less obvious signs of respiratory disease can lead to a more complete diagnosis and a more targeted treatment plan.