PSSM and the muscle metabolism — why fat replaces starch

Polysaccharide storage myopathy (PSSM) is a disorder of the muscle metabolism in which the skeletal muscle stores unusually much glycogen — the storage form of glucose — and in part also an abnormal, hard-to-break-down polysaccharide form. The consequence can be exercise-related muscle problems, in everyday language often described as tying-up.

Two forms are distinguished. PSSM1 rests on a point mutation in the GYS1 gene that codes glycogen synthase — this mutation can be detected directly via a validated genetic test. PSSM2 is the fuzzier category: it bundles myopathic pictures with a similar muscle histology for which no uniform, secured genetic test exists. This fuzziness is important before one speaks of a diagnosis.

Why fat replaces starch

The central feeding idea follows directly from the metabolism: if less starch and sugar are fed, less glucose reaches the muscle cell, and the insulin stimulus drops. Fat instead supplies free fatty acids as an alternative energy carrier for the aerobic work. In controlled feeding studies in PSSM horses, a starch-low, fat-focused ration markedly normalised the muscle enzyme values after exercise compared to a starch-rich ration.

Just as decisive as the ration is movement. Regular, daily work improves the substrate utilisation in the muscle — even short, consistent sessions are regarded as an effective building block. Long box rest, by contrast, works counterproductively. Ration and movement are no either-or here, but mesh together.

Linseed as a fat-rich, starch-low source

If energy is to come via fat rather than via grain starch, fat-rich and at the same time starch-low components are needed. Linseed (ground or as oil) supplies exactly this profile and incidentally shifts the fatty acid ratio towards omega-3. The changeover should be built up gradually and embedded in a fully calculated overall ration — a fat source alone replaces no ration planning.

Vitamin E flanks the concept antioxidatively. Stressed muscle cells are exposed to oxidative stress, and vitamin E is the most important fat-soluble antioxidant of the cell membrane. A sufficient supply is regularly considered in muscle management, especially in horses without pasture access. This is nutritional-physiological flanking via a supplementary feed, no intervention in the genetic cause.

The most robust message is at the same time the most sober: a considerable share of affected horses benefits noticeably when ration and movement come together consistently. The lever lies not in a single powder, but in a held-through line — starch-low, fat-focused, moved daily.