Equine asthma is defined as chronic inflammation of the lower airways. This can be caused by environmental allergens that include grasses, weeds, trees, dusts, molds, and toxic gases such as ammonia.  

Airborne particles can be inhaled into the respiratory tract, causing irritation and inflammation that can present as a respiratory allergic response.

There have been many prior names for equine asthma such as chronic obstructive pulmonary disease (COPD), recurrent airway obstruction (RAO), inflammatory airway disease (IAD), and heaves. However, the current terminology encompasses these as ‘equine asthma.’

Presentation of Equine Asthma

Presentation of equine asthma can vary from a slow, insidious onset to acute respiratory distress. The most common clinical presentation, however, is a horse that has ‘allergies’ in the form of mild respiratory signs that are typically seasonal. The respiratory signs can become more pronounced over the years or develop into a sudden acute presentation of difficulty in breathing.

Asthma is caused by inflammation that leads to constriction of the small airways within the lower (deeper) part of the lung. That causes difficulty in expelling air from the lungs.

In more severe cases, horses will use their diaphragm to “push” the air out, leading to development of muscular hypertrophy (enlarged muscles) and the so called ‘heave line.’

In less-severe cases, horses might present with elevated breathing at rest, nostril flare, and sometimes a cough. Exercise intolerance and poor performance more general signs that a horse suffering from asthma.

Diagnosis

Diagnosis of equine asthma requires a good clinical examination with a thorough respiratory investigation to rule out any infectious causes of respiratory disease.

If equine asthma is suspected, a bronchoalveolar lavage (BAL) can be performed to confirm the diagnosis. In this procedure the horse is sedated and small flexible tube is passed into the lungs. By isolating (effectively blocking) a small portion of the airway, sterile saline can be administered and aspirated through the tube providing an ‘airway lavage’ sample.

This sample is then spun down into a pellet of cells. These cells are examined by a clinical pathologist.

There are many different cell types that contribute to the inflammation. The type of asthma is described by the cell type found on such an examination (i.e., cytology). This might include neutrophilic or mast-cell mediated associated equine asthma.

Understanding the underlying cell type can help to guide the treatment.

Treatment of Equine Asthma

Treatment of equine asthma requires medication to reduce the level of inflammation in the airway. Environmental management is critically important in order to have a successful outcome.

Medical treatment consists of either systemic or inhaled anti-inflammatories (steroids) and bronchodilators (which help to open the airways).

There are many options for treatment. The treatment decision is based on severity of the disease, cell type, and how easy it can be to administer the medication.

Inhalers can be used to administer bronchodilators and steroids. They are generally well-tolerated. Nebulizers can also deliver saline and other liquid medications into the lower airway if appropriate. Antihistamines can also be used to help reduce the allergic response, but they are often not effective in more severe cases of equine asthma.

Allergy testing can be useful to determine if the horse is having a significant response to its environment. However, it is often non-specific to a causative allergen. Caution should be used not to over-interpret serum allergy testing as it can show the overall level of response to environmental allergens, but cross-reactivity between allergens makes it difficult to pinpoint the exact cause of the response.   

Desensitization to environmental allergens from serum testing has shown to be beneficial in cases of equine asthma. That can be used as part of the treatment plan.

Management Changes

Environmental allergen exposure is the most critical piece to successful treatment of equine asthma. Remember, allergen exposure is the inciting cause.

Most often, the allergen exposure is related to a barn environment. Horses with asthma tend to do better housed outside for at least a good portion of the day.

However, there are some equine asthma cases that are ‘pasture associated.’ Therefor, the horses are worse outside when exposed to those allergens.

Check out the below general recommendations for horses with equine asthma.

Barn Management

  1. Chose a stall with good airflow typically at the end of the barn—good ventilation is key.
  2. Don’t have any hay/bedding storage above or close to the horse’s head as allergens from the hay cause constant exposure.
  3. Do not sweep or blow the aisleways when the horses are in the stall.
  4. Consider using low-allergen beddings (e.g., good-quality paper).
  5. Remember that if rubber matting is used under bedding, it is important to lift this regularly and hose the area down plus disinfect the stable floor.  
  6. Try and keep the horse in a stall with good drainage to reduce urine buildup.
  7. In general, keep the horse’s stall as clean as possible (‘deep litter’ beds are not recommended).
  8. Remove the horse from the stall when you muck out (or muck out nearby stalls) and let the ‘dust’ settle before returning the horse to its stall.
  9. Where possible, groom outside or in a well-ventilated area.
  10. Ensure the barn/stable yard is kept as clean and dust-free as possible.
  11. For non-pasture-associated asthma, exercising outdoors when possible and avoiding dusty arenas that can exacerbate the response can be beneficial. Wetting the footing prior to riding can help reduce airborne particles from the footing.

Feed and Forage Management

  1. Start with good. hygienic-quality forage.
  2.  Soak in clear water (for about 30 minutes), drain appropriately, then feed as soon as possible. You also can steam the forage (it needs to reach the correct temperature throughout) to reduce inhaled allergen exposure. Consider feeding alternative preserved forages such as haylage.
  3. Ground positioned slow hay feeders can help avoid horses from putting their whole nose deep into the pile of hay, but they still enable the horse to forage with its head down.
  4. Ideally do not use large round bales. They often have more molds, and horses tend to put their heads into the round bale.
  5. If you must have a round bale, use a cover such as a hay net so the horse can’t stick its head into the round bale.
  6. Consider soaking your complementary feed.
  7. Consider consulting a nutritional advisor to ensure that you are not feeding excessive protein. This is especially important for animals kept in stalls for long periods as the excessive protein is removed from the body as urea in the urine, which in turn is broken down by the bacteria in the bedding to make ammonia.
  8. Maintain good hygiene in your feed and forage storage areas.

Allergy Testing

  1. Often horses that move from one area to another or move to a different country are exposed to allergens they have never seen before.
  2. Allergy testing can determine the level of exposure, but it is non-specific
  3. Desensitization can afford a longer-term solution to reduce the seasonal response to allergens every year.

Final Words

If you suspect your horse has equine asthma, consult with your veterinarian and ask her/him to perform a thorough respiratory examination. Most importantly, consider how you can make the necessary environmental changes that can help reduce allergen exposure. This is the most beneficial change for the control of asthma.

Further Reading

  • Amy C. Polkes, DVM, DACVIM, is a private practitioner in equine internal medicine active in New York, Connecticut, Maryland, Virginia, and Colorado. She also is the Medical Director of the equine division of Antech Diagnostics.
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