PSSM & Muscular Health

By: Dr. Lydia Gray

SmartPak strongly encourages you to consult your veterinarian regarding specific questions about your horse's health. This information is not intended to diagnose or treat any disease, and is purely educational.

Brief Description

Polysaccharide Storage Myopathy (PSSM), also called Equine Polysaccharide Storage Myopathy (EPSM), is an inherited condition that occurs most commonly in Quarter Horses, draft horses and warmbloods, but can also show up in other breeds. The muscles of a horse with PSSM are unable to properly store glucose (sugar), so it is unavailable when needed for energy. PSSM is related to “tying up”, but “tying up” can have many causes. For more information on the causes of “tying up” not related to PSSM, click here.

Supplements that May Lend Support

Because of the oxidative stress associated with this disorder, as well as the free radicals generated from the high fat diet often required by horses with PSSM (see ‘Diet’ below), experts recommend supplementing with Vitamin E for its antioxidant properties. Other antioxidants include Vitamin C, Grape Seed Extract and Super Oxide Dismutase. Anecdotal evidence also suggests that the anti-inflammatory/antioxidant Dimethylglycine (DMG) may be beneficial for horses with muscle disorders like PSSM.

Possible Diagnostic Tests

Signs of PSSM can range from the classic stiffening up and reluctance to move associated with “tying up”, to subtle changes in stride, difficulty backing or picking up hind limbs, loss of muscle mass, and others. The usual blood tests for “tying up” may or may not be helpful. Muscle biopsy has been the only means of truly diagnosing PSSM until very recently, when a DNA test that can be performed on mane or tail hair became available.

Prescription Medications Available

At this time, there are no prescription medications approved by the FDA for PSSM. Depending on the severity of signs, your veterinarian may administer pain relievers, fluids, sedatives or other medication to provide comfort and assist in recovery after an episode.

Other Management Suggestions


Since horses with PSSM are unable to process sugars and starches properly, fat should be used as their main source of energy. Feed companies have created several low-sugar, high-fat commercial feeds that are intended for horses with metabolic conditions such as PSSM. Other dietary suggestions include limiting access to pasture, providing low sugar hay (less than 15% Non-Structural Carbohydrates), and supplementing with additional sources of fat and other nutrients as needed. These extra fat sources can include rice bran, flax seed, vegetable oil, and powdered fat supplements. For horses receiving little to no fortified grain, a multi-vitamin/mineral supplement may also be needed.

Housing & Exercise

Ample turnout is essential for horses with PSSM, as they should not be stalled for more than 12 hours at a time. Another key to managing this condition is keeping the horse in a consistent exercise program – meaning controlled exercise such as hand walking, lunging or riding. When returning the horse to work after a bout of PSSM, start gradually. Always provide these horses with a long warm-up and cool-down, and offer frequent walk breaks.

Questions to Ask Your Veterinarian

  • How is this different from “tying up”?
  • Does my horse have to be diagnosed with PSSM or can I just begin feeding the recommended diet?
  • Will my horse return to his former level of performance?

Additional Resources

Further Reading for You

From our site:
Polysaccharide Storage Myopathy
From the SmartPak Ask the Vet Blog:
How to Prevent Polysaccharide Storage Myopathy (PSSM) in your horse
Fat Supplements with Grain
From The Horse Journal:
  • Groundbreaking Tests for EPSM, April 2008

Further Reading for Your Veterinarian

McCue ME and Valberg SJ. Estimated prevalence of polysaccharide storage myopathy among overtly health Quarter Horses in the United States. J Am Vet Med Assoc. 2007 Sep 1;231(5):746-750.

Valberg SJ. Polysaccharide storage myopathy, in Proceedings: Annu Conv Am Assoc Equine Pract 2006;52:373-38.

Valberg SJ and Mickelson JR. The interplay of genetics, exercise and nutrition in polysaccharide storage myopathy, in Proceedings: Am Coll Vet Int Med 2007:163-165.

About Dr. Lydia Gray

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