Differential diagnosis and nutritional management of equine exertional rhabdomyolysis

Exertional rhabdomyolysis (ER) has been recognized in horses for more than 100 years as a syndrome of muscle pain and cramping associated with exercise. Recently it has been recognized that this syndrome has numerous possible causes. Sporadic forms of ER are due to over-training and muscle strain, dietary deficiencies of electrolytes, vitamin E and selenium or exercise in conjunction with herpes or influenza virus infections. Chronic forms are due to specific inherited abnormalities such as polysaccharide storage myopathy (PSSM) in Quarter Horses, Warmbloods and Draft breeds or recurrent exertional rhabdomyolysis (RER) in Thoroughbreds, Standardbreds and Arabians. PSSM, a glycogen storage disorder, can effectively be managed by providing regular daily exercise and a high fiber diet with minimal starch and sugar and provision of a fat supplement. RER appears to be a disorder of intracellular calcium regulation that is triggered by excitement. Changing management to provide horses with a calm environment and training schedule and substitution of fat for grains in high caloric rations are helpful means to manage this condition.