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“Roarers” are horses that make unusually loud noise as their breathing becomes faster and deeper with increasing exercise. Roaring is caused when one or both arytenoid cartilages in the throat become paralyzed and partially block the airway instead of being automatically retracted as the horse breathes.

According to Bryan Waldridge, D.V.M., staff veterinarian for Kentucky Equine Research, this paralysis is more common on the left side of the horse’s throat and is termed left-sided laryngeal hemiplegia. Treatment of the condition involves tie-back surgery in which the cartilage is pulled to the side and sutured to keep it from interfering with the flow of air. In some horses, the vocal cords are also removed (ventriculocordectomy) to increase airflow and reduce noise as the horse breathes.

Horses usually breathe better after surgery, but in some cases, horses have had an increase in inflammatory airway disease (IAD) and exercise-induced pulmonary hemorrhage (EIPH) following tie-back procedures. A study conducted in Hong Kong was designed to investigate the incidence of these problems in horses that had left-sided prosthetic laryngoplasty and ventriculocordectomy (PLVC).

A study group was composed of 24 horses that had undergone this surgical treatment for roaring. Each horse in the study group was matched with two horses that were not roarers. These control horses were matched to study group horses by trainer, year of import into Hong Kong, and international handicap rating. Horses in the control group were all Thoroughbred racehorse geldings with an average age of three years.

Prior to surgery, horses in both groups had similar levels of EIPH. After surgery, all surgical horses showed some degree of EIPH. Epistaxis, a severe degree of EIPH in which blood drips from the nostrils after exercise, was seen in 38% of surgical horses compared to only 7% of control horses. All surgical group horses also showed excess tracheal mucus after surgery, a condition that was seen in only 32% of control horses.

After treatment, surgical horses had fewer race starts than horses in the control group, though the number of starts for which stakes money was earned was not significantly different. Among horses that had surgery, 70% were retired from racing within two years. Retirement was primarily because of epistaxis. Of the control horses, only 37% retired in same time period.

The authors of the study report that while tie-back surgery does result in a less obstructed flow of air in exercising horses, it does not produce a completely normal airway. Surgical procedure could make horses somewhat more susceptible to inflammation and infection, and some degree of airway obstruction could still be present. It was concluded that horses undergoing this surgery might be at higher risk for EIPH, excess tracheal mucus, and shorter racing careers compared to healthy horses that are not treated by surgery. However, the surgery does greatly improve airflow in some horses, many of which can resume a successful racing career after recovery.

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