Causes of poor performance of horses during training, racing, or showing: 348 cases (1992-1996)

Objective-To determine results for horses undergoing a high-speed treadmill examination, including videoendoscopy of the pharynx and larynx before and during exercise, echocardiography before:and after exercise, and electrocardiography before, during, and after exercise, because of poor performance. Design-Retrospective study. Animals-348 horses. Results-A definitive diagnosis was obtained for 256 [73.5%) horses. One hundred forty-eight horses had dynamic obstruction of the airway during exercise, 33 had clinically important cardiac arrhythmias alone, 22 had a combination of dynamic airway obstruction and clinically important cardiac arrhythmias, 19 had poor cardiac fractional shortening immediately after exercise, 10 had exertional rhabdomyolyis, 15 had clinically apparent lameness,and 9 had other disorders. Thirty-nine of the horses with dynamic obstruction of the airway during exercise had multiple airway abnormalities. Fifty-three horses also had subclinical myopathy. Conclusions and Clinical Relevance-Results suggest that a complete evaluation, including-a. highspeed treadmill examination, should be conducted in horses with poor performance, regardless or whether horses do or do not have a history of abnormal respiratory noises and particularly if the horse shave grade-II or -III left laryngeal hemiplegia.