Understanding Summer Pasture-Associated Recurrent Airway Obstruction in Horses
Recurrent Airway Obstruction (RAO), often referred to as heaves, is a common condition in horses that affects the respiratory system, causing difficulty in breathing and discomfort. While RAO can occur year-round, it is particularly prevalent during the summer months, especially in horses exposed to pastures where there are high levels of airborne allergens. This condition is one of the most prevalent equine respiratory disorders and can significantly affect a horse’s overall health, performance, and quality of life.
In this article, we will discuss summer pasture-associated RAO in horses (SPARAO), focusing on its causes, clinical signs, treatment, and management strategies. To know more on Equine Asthma in general click here.
What Causes Summer Pasture-Associated RAO?
Summer pasture-associated RAO is triggered by exposure to specific allergens found in grasses, mould, and dust that are more abundant during warmer months. Unlike the typical environmental triggers of RAO, which may involve exposure to hay, straw, and bedding, pasture-associated RAO is linked to particular conditions found in outdoor environments during the summer. These conditions include:
- Pollen: Many grasses, trees and other plants release pollen during the summer months. Pollen is a known allergen and can be inhaled by horses grazing in the pasture.
- Mould: Pastures with high humidity can harbour mould in the soil or on plants, and mould spores are a significant irritant to the respiratory system.
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Dust: Dry and hot summer weather often leads to dusty conditions, particularly when horses are grazing or exercising on pastures. Dust contains particulate matter that can irritate the lungs and trigger an inflammatory response.
The underlying cause of RAO is a hypersensitivity or allergic reaction in the horse’s airways. These allergic reactions cause inflammation, bronchoconstriction (narrowing of the airways), and excessive mucus production, which makes breathing more difficult.
Clinical Signs of Summer Pasture-Associated RAO
The clinical signs of summer pasture-associated RAO can range from mild to severe, depending on the extent of airway obstruction. Horses with RAO typically exhibit respiratory distress, which can manifest in various ways:
- Coughing: One of the hallmark signs of RAO is coughing, particularly after exercise or during exposure to dust or pollen. The coughing may be persistent and worsen as the condition progresses.
- Nasal Discharge: A horse suffering from RAO may develop a nasal discharge. This is due to increased mucus production in the airways as a result of inflammation.
- Laboured Breathing: As the condition worsens, horses may exhibit signs of laboured or difficulty breathing. This may include flared nostrils, an increased respiratory rate, and noticeable effort when exhaling.
- Heave Line: A distinct "heave line" can sometimes develop along the horse’s abdomen. This is a visible muscle ridge caused by the excessive use of abdominal muscles to help expel air from the lungs during laboured breathing. (photo would be good)
- Exercise Intolerance: Horses with RAO may show a marked decrease in their ability to exercise, as the condition causes them to tire quickly and suffer from shortness of breath. Work can also trigger coughing episodes, particularly at the start of exercise.
- Poor Coat Condition: In chronic cases, RAO can lead to a dull, rough coat due to the horse’s overall poor health and decreased ability to groom itself properly.
Diagnosis of RAO
If you suspect a horse has RAO, a thorough veterinary examination is crucial. The diagnosis typically involves the following steps:
- History and Clinical Signs: Your vet will first assess the horse’s history, including its exposure to potential allergens, seasonal patterns, and clinical signs like coughing or exercise intolerance.
- Endoscopy: This involves inserting a flexible tube into the horse’s airways to observe the condition of the respiratory tract. This can help identify inflammation and mucus build up.
- Tracheal Wash (TW) or Bronchoalveolar Lavage (BAL): A TW or BAL are diagnostic procedures where a small amount of fluid is introduced into the lungs and then withdrawn to collect cells and mucus. The presence of inflammatory cells is indicative of RAO.
- Blood Work: Blood tests may be used to evaluate inflammation levels in the horse's body and check for any systemic involvement.
Treatment of Summer Pasture-Associated RAO
While there is no cure for RAO, treatment can help manage the condition and alleviate symptoms. The primary goals of treatment are to reduce inflammation in the airways, improve airflow, and control triggers like allergens. Treatment options include:
- Bronchodilators: Medications that relax the muscles of the airways, allowing the horse to breathe more easily. Common bronchodilators include clenbuterol. These are usually given by injection or orally by mouth/in feed.
- Corticosteroids: These medications are used to reduce inflammation in the airways. They can be administered orally, intravenously, or by inhalation. Inhaled corticosteroids may be preferred because they deliver the drug directly to the lungs with fewer side effects.
- Antihistamines: These medications may be used to control allergic reactions by blocking the action of histamine, a chemical involved in allergic responses. Results are less predictable than for other species such as humans, so they can be less effective in horses.
- Antibiotics: If a secondary bacterial infection is suspected, antibiotics may be prescribed, though these are not typically used unless there is evidence of infection.
Management of Summer Pasture-Associated RAO
In addition to medical treatments, managing the environment and reducing exposure to allergens is key to preventing and controlling RAO. Here are some management strategies:
- Limit Pasture Time: Reducing the time the horse spends in pastures with high levels of allergens can help manage symptoms. Consider bringing the horse indoors during peak pollen times, or when the pasture is particularly dusty.
- Provide Dust-Free Feed and Bedding: Offering hay that has been soaked or steamed can reduce the level of dust and mould. Although not typically a cause of summer pasture-associated RAO, any extra dust in the environment can exacerbate signs.
- Use of Dust-Free Stabling: Keeping the horse in a well-ventilated stable that is free from dust and mould can help minimize symptoms. Avoiding straw bedding and opting for a more breathable material can also be beneficial.
- Environmental Control: For horses with severe symptoms, installing air purifiers or using misting systems in the barn can help reduce airborne allergens. Maintaining clean stables and pastures by removing wet or spoiled bedding and plants can also be crucial.
- Exercise Modifications: For horses with exercise intolerance, reducing the intensity or frequency of exercise may be necessary to prevent respiratory distress. Additionally, avoiding exercise during high pollen or dust periods can be beneficial.
- Nutrition: Research shows that providing a targeted feed supplement, designed for respiratory health, and based on natural antioxidants can be a useful tool within your horse’s clear airway regime.
Conclusion
Summer pasture-associated recurrent airway obstruction is a challenging condition that can affect a horse’s ability to perform and enjoy normal activities. Understanding the causes, recognizing the clinical signs, and implementing effective treatment and management strategies are essential to ensuring that affected horses can continue to lead healthy and active lives. By addressing environmental triggers, providing appropriate medical treatment, and supplementing with targeted nutritional support, owners can help manage this condition and improve the quality of life for their horses.
If you suspect your horse may be suffering from RAO, consult your vet for an accurate diagnosis and tailored treatment plan to best support your horse’s respiratory health.
Selected References
- Couëtil LL, Cardwell JM, Gerber V, Lavoie JP, Léguillette R, Richard EA. Inflammatory Airway Disease of Horses--Revised Consensus Statement. J Vet Intern Med. 2016 Mar-Apr;30(2):503-15.
- Kirschvink N, Fiévez L, Bougnet V, Art T, Degand G, Smith N, Marlin D, Roberts C, Harris P, Lekeux P. Effect of nutritional antioxidant supplementation on systemic and pulmonary antioxidant status, airway inflammation and lung function in heaves-affected horses. Equine Vet J. 2002 Nov;34(7):705-12.
Written by: Dr Andy Richardson, Veterinary Director. BVSc Cert AVP(ESM) MRCVS.
