roaring (laryngeal hemiplegia)

A whistling sound made by a horse during inhalation while exercising. It is caused by a partial or total paralysis of the nerves controlling the muscles which elevate the arytenoid cartilages which thereby open the larynx. In severe cases, a surgical procedure known as "tie-back surgery" (laryngoplasty) is performed, in which a suture is inserted through the cartilage to hold it out of the airway permanently. Paralysis almost exclusively occurs on the left side, most frequently in horses over 16 hands high.