If your horse has a cough – even if it’s just a couple as you start trotting – take action.
Horses can have significant lung inflammation before they cough, so once they actually cough, there is a problem.
Any persistent cough needs veterinary attention, since its cause needs to be determined. If the cough is due to a dust/forage allergy, your horse may need medication as well as an environment change, and nowadays more effective inhaled medication is available, compared to the oral medication used in the past.
If your horse has dust/forage allergies (RAO, or recurrent airway obstruction, which used to be called COPD):
Consider the amount of turnout (ideally maximise) and ventilation in the stable
Ensure dust-free stable bedding and clean out the stable (including any banks) daily (no deep litter). Clean the walls and ceiling of the stable regularly
Consider the forage both in the stable and outside in the pasture. Soak hay for at least 10 minutes, totally submerged, or feed haylage
Add water to dampen dust in bucket feed
Consider an antioxidant-rich respiratory supporting supplement