A respiratory noise during exercise occurs when there is an anatomical or functional obstruction of the upper respiratory tract (area from the nose to the back of the throat).
These problems can be a challenge to diagnose accurately as some abnormalities may only be visible in the upper respiratory tract while the horse is exercising and at rest the upper respiratory tract may look normal. The most common conditions causing respiratory noise are problems of the epiglottis (part of the larynx at the back of the throat, the soft palate and laryngeal hemiplegia.
To make a diagnosis requires endoscopy (looking down nasal passages and trachea and into the lungs), however, as many horses are normal at rest an endoscopic examination during exercise with the horse on a treadmill may be required. The causes of respiratory noise during exercise can sometimes only present as reduced performance of the animal without a noise being audible. In these cases it is worth performing endoscopy, as explained above, if no other causes of reduced performance can be found.