ABSTRACT
Exertional rhabdomyolysis has been recognized in horses for more than 100 years as a syndrome of muscle pain and cramping associated with exercise. In the last ten to twelve years, research advances have provided greater insight into this syndrome. Of greatest importance is the realization that exertional rhabdomyolysis comprises several myopathies that, despite similarities in clinical presentation, differ considerably in regards to pathogenesis (cellular events, reactions, and other pathologic mechanisms occurring in the development of disease). Tying-up is a common disorder in Thoroughbred racehorses. During the 1995 racing season, 1000 Thoroughbreds at Canterbury Park were evaluated. Five percent of the horses exhibited signs of tying-up during the season. Of the two- and threeyear-old horses that presented with tying-up, 15% could not be raced at all that season. Interestingly, if the horses that experienced tying-up could race, there was no difference between their performances and those of matched control horses. Exertional rhabdomyolysis continues to be a performance-limiting or careerending disorder for many equine athletes. Advances in the management of horses with exertional rhabdomyolysis, particularly in the way they are fed, have significantly reduced the impact of the disorder.