If you see hay that has the slightest bit of mold, get rid of it immediately. [substeps] Store your hay in a place that is protected from the elements, but not directly in or above your horse's stall, since this can expose the animal to allergens.
[header] How to treat allergies in horses [title] Don't feed your horse moldy hay. [step] Recurrent airway obstruction (rao), or " heaves, " is a respiratory condition in horses that can cause coughing and other issues. The condition is caused by irritating spores that can develop in moldy hay.