Muscular and Skeletal Illnesses in Horses

By PetMD Editorial on Oct. 1, 2008

Equine Polysaccharide Storage Myopathy


Equine Polysaccharide Storage Myopathy (EPSM) is an illness that affects the skeletal and muscular systems in many of the stockier horse breeds. Among those breeds affected are the American Quarter and Paint horses, as well as Warm Bloods and any horse that is cross-bred with the aforementioned breeds. Generally, the heavier the horse is, the more serious the condition is. EPSM is also more likely to affect mares than male horses.




A horse with EPSM will usually avoid exercise, lay down frequently, and be reluctant to move altogether. It will have muscle pain in its gluteal, bicep or hind leg regions, which results in uncontrolled twitching or “attacks.” These “attacks” commonly occur shortly after the horse's exercise routine has begun, but may occur at random as well. Some other common symptoms include:


  • Strange gait
  • Trouble keeping its balance
  • Stiffness in legs
  • Abnormal flexion in one or both back legs
  • Severe weight loss/muscle wasting
  • Thinness in the rump/thigh area
  • Heightened level of certain enzymes (i.e., Creatininekinase, Lactate dehydrogenase, Aspartetransaminase)




There has been substantial research done to discover the cause of EPSM, and it is now thought genetics may play a large part in the transmission of the illness. Some horses fail to produce glycogen properly in their muscles, allowing large amounts of polysaccharides to collect inside the muscles. In essence, the muscles have no fuel to perform.




In order to properly diagnose EPSM, a veterinarian will likely perform a muscle biopsy of the affected area on the horse.




Unfortunately, there is no treatment for EPSM that has proven to be truly effective. However, there are changes that can be made to a horse’s diet and exercise routine that can help it perform and live a normal life. Such changes include eliminating all unnecessary carbohydrate concentrates from its diet, including sugar beets, molasses, grain, etc. Instead, consult your veterinarian as to what high quality roughage can be given as a replacement.


Living and Management


As far as exercise is concerned, the horse must begin slowly before achieving thirty minutes of “real” exercise. This should be done once per day. While you may be inclined to allow it to rest comfortably in the stable, too much rest can be detrimental to the horse's health and performance. Instead, your EPSM-diagnosed horse should be kept out in the pasture (and out of the stable) as much as it will allow for.

Help us make PetMD better

Was this article helpful?

Get Instant Vet Help Via Chat or Video. Connect with a Vet. Chewy Health