Respiratory noises are most commonly heard at faster gaits, such as the canter or gallop.
A horse who emits rasping, whistling or other respiratory noises when he gallops may have a condition called roaring, technically known as laryngeal hemiplegia.
Roaring occurs when the muscles on one or both sides of the larynx are weak or paralyzed. As a result, the cartilages in the larynx (arytenoids) and the vocal cords sag into or even block the airway (trachea), restricting breathing and producing a roaring sound. Trauma, neurological damage or infection can precipitate roaring, but most cases have no known cause.
If you suspect your horse is a roarer, call your veterinarian, who will use an endoscope to make a diagnosis. In addition, be prepared to answer some questions that can help the investigation.
• What do you hear? Laryngeal hemiplegia produces noises that range from a loud rasping and whistling to a soft purring or snoring sound. The greater the airway blockage the more high-pitched and loud the noise becomes. Some roarers also cough during exertion.
• When does the sound occur? Roaring usually happens as the horse inhales when galloping because damaged arytenoids cannot open wide enough to draw in the air needed for exertion. A headset that results in extreme flexion at the poll can also trigger the noise.
• Is your horse’s performance affected? A roaring horse may tire easily and take longer than expected to catch his breath after a gallop. If the larynx is completely blocked, he might seem to panic, “shutting down” and pulling himself up.