Thanks to advances in identifying specific causes of tying-up, development of diagnostic tests, and improved recognition of the impact of diet and exercise on horses that tie up, affected horses can be successfully managed. Stephanie Valberg, DVM, PhD, professor of large animal medicine and director of the University of Minnesota's Equine Center, relayed this message during her talk "The Management of Tying-Up in Sport Horses: Challenges and Successes" presented at the 2010 Kentucky Equine Research Nutrition Conference held April 26-27 in Lexington.

Tying-up (exertional rhabdomyolysis) is a relatively common condition of skeletal muscle tissues characterized by muscle pain, a stiff, stilted gait, excessive sweating, and distress. A wide variety of breeds are affected, including warmbloods, Thoroughbreds, Standardbreds, Arabians, Morgans, Quarter Horses, Appaloosas, and Paints.

"To date, multiple causes of muscle diseases have been identified that vary from something as innocuous as lack of conditioning to more serious genetic abnormalities such as hyperkalemic period paralysis (HYPP), glycogen branching enzyme deficiency (GBED), malignant hyperthermia (MH), and type 1 polysaccharide storage myopathy (PSSM1)," explained Valberg.

Nutritional factors are known to impact tying-up. For example, horses fed a high grain diet appear more likely to tie up than horses fed a low-grain or fat-supplemented diet. Further, electrolyte depletion in athletic horses and potentially low selenium and/or vitamin E levels are also thought to contribute to the development of sporadic cases of tying-up