By: Dr Rosie Alcorn BVSc PG Cert VPS Cert AVP MRCVS
Managing horses with Polysaccharide Storage Myopathy (PSSM) requires a comprehensive approach that includes diet, exercise, and careful monitoring. PSSM is a muscle disorder in horses that affects how glycogen (a form of stored sugar) is used and stored in the muscles.
There are two main types:
PSSM Type 1 (PSSM1): Caused by a genetic mutation (GYS1 gene).
PSSM Type 2 (PSSM2): Muscle dysfunction not linked to the GYS1 mutation and less well understood.
Low-starch, low-sugar diet: Critical for reducing the amount of glucose entering the muscle.
◦ Eliminate or greatly reduce grain, molasses, sweet feeds, and pasture turnout (especially lush grass).
High fat: Fat provides an alternative energy source for muscle cells.
◦ Add fat sources such as oil or rice bran.
Forage first: Feed high-quality hay with NSC (non-structural carbohydrates) below 12%.
Electrolytes & minerals: Balanced levels of vitamin E, selenium, and electrolytes are often beneficial. Consider a full ration balancer or custom supplementation.
High-quality protein: Ensure adequate protein is available to maintain and repair muscle tissue.
Golden Oldies is a low sugar, low starch veteran balancer mash which is specifically formulated to meet the needs of older equines. Being cereal free and very low sugar and starch widens the suitability to any horse or pony with PPID, EMS, PSSM etc.
Consistency is key: Regular, daily exercise helps prevent tying-up.
◦ Even 10–15 minutes of consistent movement (e.g., hand-walking) is beneficial.
Gradual warm-up and cool-down: Reduces the risk of tying-up.
Avoid prolonged rest: Days off can lead to worsening of symptoms when the horse returns to work.
Minimise stress: Changes in routine, transport, or new environments can trigger episodes.
Rug up in cold weather: Helps prevent cold-induced muscle stiffness.
Turnout: Frequent or full-time turnout with room to move is ideal, assuming pasture sugar levels are controlled.
Regular bloodwork (CK, AST) during transitions in diet or exercise.
Muscle biopsy or genetic testing for diagnosis and subtype confirmation.
Some horses with PSSM2 may respond to supplements such as vitamin E, omega-3s, or amino acids, especially if muscle soreness is present.
Muscle stiffness or cramping
Reluctance to move or exercise intolerance
Sweating, shifting weight, or muscle tremors
Tying-up episodes after rest or high-starch meals
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