In search of the best surgical method to treat roaring in horses

Abstract

While few accurate statistics are available, veterinarians, horse owners and trainers report that respiratory disease is second only to lameness as a cause of reduced performance in athletic horses. Roaring (left laryngeal hemiplegia) is one of the more serious respiratory conditions affecting horses and it has been estimated that up to 5 percent of all Thoroughbreds develop the condition. The disease prevalence is greatest in the three to seven year age group when affected horses are at the peak of their athletic performance. Roaring results in significant exercise intolerance and noise production on inhalation and the disease has devastated the aspiration of many horse owners. Veterinary surgeons have developed a series of surgical techniques to relieve the laryngeal obstruction caused by roaring. Surgical interventions include ventriculectomy, prosthetic laryngoplasty and subtotal left arytenoidectomy. In spite of the common occurrence of left laryngeal hemiplegia and the frequency of surgical intervention in the disease, the effects of left laryngeal hemiplegia on upper airway flow mechanics during exercise or efficacy of surgical intervention had not been documented. Surgical success rates have been published frequently but are based on subjective criteria. Before the results of the author's MAF-sponsored study were published, the veterinary surgeon had no solid basis on which to select the most appropriate surgical intervention in cases of roaring. Clearly a quantitative comparison of the efficacy of commonly used surgical interventions in roarers was needed. Therefore with the help of the Morris Animal Foundation, the author and colleagues set out to evaluate the effect of roaring on airway flow mechanics in exercising horses and to compare the efficacy of surgical repair by prosthetic laryngoplasty and by ventriculectomy. At present we are in the process of evaluating the arytenoidectomy technique, but the results of this part of the study are not yet available. We found that horses with left larynegeal hemiplegia have no respiratory problems at rest, but when exericising vigorously, they use up to ten times as much effort to move air into the lungs. Ventriculectomy, a procedure that has been commonly used to treat roarers since the 18Pr3's failed to reduce the work of breathing in exercising horses with the condition. However, prosthetic laryngoplasty, a newer procedure, completely prevented the respiratory difficulties associated with roaring. Combining the two surgical prodcures, a technique commonly used at present, had no advantage over the use of prosthetic laryngoplasty alone. Therefore, this study has clearly identified prosthetic laryngoplasty as the technique of choice to treat roaring in horses. From MAF )