Equine Polysaccharide Storage Myopathy, or PSSM, affects many types of horses including quarter horses, paint horses, appaloosas, draft horses and warmbloods. Horses with PSSM are not able to properly convert carbohydrates into energy. The un-metabolized carbohydrates collect in the muscles and cannot be utilized for muscle function. The result is mild to severe muscle damage or even death, depending on how far the condition has progressed. PSSM is the likely cause of “Monday Morning Disease” — when horses that have taken a day off from exercising have difficulty moving around once they begin exercising again.
Symptoms of equine PSSM include muscle atrophy, brown urine, stiffness, difficulty getting up, trembling after exercise, and cramping. Horses may not show symptoms for years, so testing will identify the condition before it becomes serious. The chances of recovery are good for horses that carry PSSM but are not showing symptoms – recovery rates decline substantially once horses have problems getting up.
Importance of Identifying PSSM
Although PSSM cannot be cured since it is a genetic disorder, muscle function can be restored with a change in diet and exercise routine. Eliminating carbohydrates such as grains and sweet feed from the horse’s diet and adding extra fat seems to alleviate the condition. However, the disorder can lead to death if it’s not identified early enough to make the necessary dietary and exercise changes, so it is vital to identify the presence of PSSM as early as possible. Additionally, identifying horses carrying the PSSM allele can assist with breeding draft horses free of PSSM.
Animal Genetics can test for the presence of PSSM alleles using DNA material from the roots of horse tail and mane hairs. To learn more about collecting DNA samples, please see the equine DNA sample collection page on our website.