The cause of PSSM or ‘tying up’ in horses

Progress has been made in the search for the cause of Polysaccharide Storage Myopathy (PSSM) – otherwise known as ‘tying up’ in horses. 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.

Symptoms of PSSM

Affected horses commonly have episodes of tying up and muscle soreness but, 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 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 projects to understand more about PSSM and Exertional Rhabdomyolysis Syndrome are ongoing.

Use a low-sugar and starch feed using fibre and oil as energy sources

In the meantime, the feeding advice for horses with both conditions remains the same: low-sugar and starch feeds using fibre and oil as energy sources. If you would like further information on this research read our article on Feeding Horses with ERS & Muscle Related Problems or contact our Dengie feedline on 01621 841188 for advice.