Seasonal recurrent airway obstruction, also known as summer pasture-associated recurrent airway obstruction (SPA-RAO), is a seasonal airway obstructive disease of horses, characterized by clinical exacerbation after exposure to pasture during the summer. Clinical signs usually present in horses during exposure to pastures during turnout in the late spring the summer, although some horses don't develop signs until late summer or early fall. Certain mold spores, grass pollens, and species of grass trigger onset of the disease.
