Recurrent laryngeal neuropathy (RLN), also referred to as roaring, is a common performance limiting neurological condition in horses. Affected horses have mild to severe blockage of the airway, evident during strenuous exercise due to the presence of 'roaring' noise and reduced athletic performance. When these horses are at rest or performing minimal exercise they are able to breathe fairly normally.
The 'roaring' noise occurs due to inadequate airflow through the horse's trachea, due to damage or weakening of the muscles and nerves responsible for opening the horse's larynx during exercise. These are known as the cricoarytenoid dorsalis (CAD) muscles, which control the movement of the arytenoid cartilages over the larynx. The exact cause of the condition is unknown, however environmental and genetic factors both contribute to disease development.
The amount of noise produced by roarers varies with the extent of airway blockage. When the airway is only slightly blocked, the sound is usually very mild and may not be any louder than a whisper. When there is significant blockage, horses will usually produce a much louder sound.
Different grading systems were developed to assess the degree of impairment. One is called the laryngeal function score (LFS) which provides a five-point scheme that is used in Europe and The Havermeyer system which uses 7 grades is used in the United States. The grading system is used during an endoscopy exam.
Surgery is the only known treatment for horses with RLN. There are multiple surgical techniques used, with varying success rates and associated complications.
A surgical procedure involving suturing the cartilage out of the way. It is usually effective for restoring free airflow, but there is a risk of recurrence if the sutures tear out or if the tissues are stretched during muscle movement around the larynx.
A surgical procedure involving severing of the nerves near the larynx.
Prognosis depends on the horse’s required level of performance and surgical treatment performed. Overall success rates ranges from 50-90%; racehorses and those with a higher demand for airflow have slightly lower success rates while show horses, draft horses, and pleasure horses tend to have higher