Feeding Horses With Muscle Issues

Horses with exertional myopathies can benefit from dietary modifications as well as consistent targeted exercise.

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Horses with exertional myopathies can experience muscle fatigue, pain, cramping, and damage. Special modifications to diet and exercise can help these horses. Stephanie Valberg, DVM, PhD, Dipl. ACVIM, ACVSMR, of the Michigan State University College of Veterinary Medicine’s Department of Large Animal Clinical Sciences described how to maintain these horses in her presentation at the 2016 American Association of Equine Practitioners Convention, held Dec. 3-7 in Orlando, Florida. She stressed that for horses to improve, they need both regular exercise and dietary management.


Valberg said recurrent exertional rhabdomyolysis (RER), also known as tying-up, is most likely caused by abnormal calcium cycling, a process that controls muscle contraction and relaxation within the muscle cell. Horses suffering from an acute episode of RER have very stiff, hard, painful muscles and are reluctant to move. Thoroughbreds, Standardbreds, and Arabians appear to be predisposed. The condition often occurs in fit animals, and is frequently triggered by stress and exercise.

Polysaccharide storage myopathy (PSSM) comes in two forms. Type 1 PSSM is caused by a mutation in the gene that regulates the body’s synthesis of the enzyme glycogen synthase, causing a buildup of glycogen (the storage form of glucose) in the muscle cell. Type 2 PSSM has no known cause, but is diagnosed via muscle biopsy revealing abnormal glycogen “clumping,” in cells. These horses do not have the genetic mutation seen in Type 1 PSSM.

Diet and Exercise: Special Care Required

The general rule of thumb with these horses is to keep nonstructural carbohydrate (NSC, starch and sugar) levels low and provide extra calories with fat. In horses with RER, Valberg recommended restricting calories provided by NSCs to less than 20% of the diet to help minimize excitability, and providing up to 20% of calories with fat. Body condition of the horse matters, as do caloric needs. Horses receiving 5 kilograms (11 pounds) or more of grain tend to be at higher risk for an episode of RER than horses receiving 2.5 kilograms (5.5 pounds) or less

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Written by:

Nettie Liburt, MS, PhD, PAS, is an equine nutritionist based on Long Island, New York. She is a graduate of Rutgers University, where she studied equine exercise physiology and nutrition. Liburt is a member of the Equine Science Society.

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