Recurrent Airway Obstruction (RAO) in Horses

Symptoms of RAO in Horses

In the early stages of RAO, or in horses only mildly afflicted with the disorder, the symptoms are generally just a slightly runny nose and dry cough. As the disease progresses, however, symptoms generally become far more severe.

Symptoms

• Chronic cough, which may bring up secretions
• Nasal discharge/runny nose
• Labored breathing
• Exercise intolerance
• "Heave line" of overdeveloped chest muscles at the bottom of the rib cage due to the strain of breathing
• Flared nostrils
• Tachypnea (breathing more rapidly than normal)
• Wheezing or rattling sounds when breathing
• Weight loss
• Lack of appetite

Initially, horses with RAO tend to experience symptoms only when exercising. However, horses with more severe disease display symptoms even when at rest. These horses have a persistent cough and often "heave" their sides in and out with the effort of breathing. You'll notice that your horse's nostrils are flared, which is an attempt to draw in air more easily, and the animal is breathing rapidly. Often, there's a yellowish nasal discharge, as well. Your horse's ability to exercise or work will greatly diminish as the disease progresses.

Horses with severe RAO may lose weight due to a lack of interest in eating. However, a fever is not a normal symptom of this disorder. Development of fever usually indicates a secondary bacterial infection, often pneumonia.1

Causes of Recurrent Airway Obstruction

Recurrent airway obstruction in horses is similar to asthma in humans and is believed to be an allergic response to inhaled antigens, primarily dust, mold spores, hay, and straw. When the horse inhales these common allergens, its airways respond by clamping shut (bronchospasm), narrowing (bronchoconstriction), and secreting mucus.

There also may be a hereditary component that contributes to a horse's likelihood of developing RAO, as horses with afflicted parents are far likelier to develop the disorder than horses with healthy parents.2

Diagnosing RAO in Horses

Generally, an equine veterinarian can diagnose recurrent airway obstruction based on the horse's characteristic symptoms and history. At times, however, your vet might want to do further testing to establish the diagnosis or rule out other causes of a chronic cough. One such test is a bronchoalveolar lavage, which involves passing a tube into the horse's lungs, "washing" the lungs with a saline solution, and then suctioning the saline back out again. This provides a sample of cells from the horse's lungs, as well as the secretions within the airways.