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New Research identifies cause of Polysaccharide Storage Myopathy (PSSM)

21st April 2008

Progress has been made in the search of a cause of Polysaccharide Storage Myopathy (PSSM) or tying up to give it one of its layman terms. PSSM is currently estimated to affect more than one-third of draft horses and one-tenth of all Quarter Horses, although it has also been diagnosed in Thoroughbreds as well.  Affected horses commonly have episodes of tying-up and muscle soreness; however in some cases, muscle atrophy (decrease in muscle size), weakness and gait abnormalities are present.  In severe cases, horses with PSSM might be unable to rise after lying down.

In the study the researchers analysed the DNA from 48 Quarter Horses with PSSM and another 48 Quarter Horses that were PSSM free.  The results identified a genetic mutation in the group of horses with PSSM.  In the gene for the enzyme called glycogen synthase (the enzyme that stimulates glycogen production), a single mutation resulted in an overactive enzyme.  Mutations that result in an increase in enzyme function are rare in all species.

This mutation results in an increase in glycogen synthesis in the muscle tissue of affected horses and a disruption in normal energy metabolism.  Research to further understand the exact metabolic steps in PSSM that cause muscle damage and exertional rhabdomyolysis (ERS)  (tying up in layman terms) are ongoing.

In the meantime the feeding advice for horses with both conditions remains the same; low sugar and starch feeds using oil as an energy source.  If you would like further information on this research please call the Dengie Feedline on 0845 345 5115 or click here to read our article on Feeding Horses with ERS & Muscle Related Problems.

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