Recurrent Airway Obstruction (RAO) in Horses
Horses have delicate lungs and are very sensitive to inhaled dust, pollen, and mold spores. Exposure to these irritants over time can lead to a persistent cough, difficulty breathing, and nasal discharge. This allergic response is called recurrent airway obstruction (RAO). Older terms still often used for this condition include chronic obstructive pulmonary disease (COPD), "heaves" or "broken wind."
RAO usually first appears when the horse is between nine and 12 years of age. Approximately 12 percent of mature horses have some degree of this respiratory affliction.1
Although RAO is a chronic condition, many horses afflicted with this respiratory problem enjoy long and relatively normal lives. However, management of these horses does require vigilance to ensure the horse isn’t overworked or exposed to allergens that trigger breathing difficulties, such as dusty hay. While there’s no cure, most horses with heaves can be comfortable and can be lightly worked. Here’s how recurrent airway obstruction develops and what you can do to help your horse.
What Is Recurrent Airway Obstruction?
Horses' lower respiratory systems, as well as the respiratory systems of other mammals, consist of a large trachea (windpipe) that branches off into two main bronchi—these are something like the stems of the lungs—which then branch further into small airways called bronchioles. Recurrent airway obstruction is an allergic response that causes inflammation in the bronchioles. Over time, this causes them to thicken and leak mucus, leading to the characteristic cough, difficulty breathing, and other symptoms of this chronic condition.
RAO is considered to be a type of equine asthma.2
While the mechanisms of RAO are not well understood, it is ultimately believed to be caused by the horse's lung's hypersensitivity to allergens, especially hay, straw, mold, and dust. Horses that live in stables and eat hay are the likeliest to develop the condition, but it can strike pastured horses as well. Typically, stabled horses with RAO have the worst symptoms in the winter and spring, while pastured horses suffer the worst symptoms in the summer or early fall.2
