Stick to High-Fat, Low-Starch Feeds for Type 2 PSSM Horses

Are feeding recommendations for horses with all types of polysaccharide storage myopathy (PSSM) effective in reducing clinical signs? This exact question was recently investigated by Stephanie Valberg, D.V.M., Ph.D., and colleagues from Michigan State University College of Veterinary Medicine.

PSSM is a muscle disorder resulting from an abnormal accumulation of glycogen—the storage form of glucose—in muscle tissues. Usually, muscle stockpiles innumerable glucose molecules in the form of glycogen, which is used for energy during muscle contraction. In horses with PSSM, too much glycogen is produced, and muscle tissues become inundated with an abnormal form of glycogen.

“Horses with PSSM show classic signs of tying-up, also referred to as exertional myopathy, including muscle pain, stiffness, and a failure to move forward under saddle, all of which translates into decreased performance,” described Laura Petroski-Rose, B.V.M.S., a veterinarian for Kentucky Equine Research.

While a clear genetic mutation responsible for type 1 PSSM exists, the underlying cause of type 2 PSSM remains elusive. Further, management of horses affected with type 2 PSSM have simply been based off recommendations for horses with type 1 PSSM due to similarities between the two conditions.

“Those dietary recommendations for type 1 PSSM horses include feeding diets low in starch and sugar and providing fat as an alternative energy source,” relayed Petroski. More specifically, horses with PSSM should be offered diets with less than 20% digestible energy from nonstructural carbohydrates and up to 25% of digestible energy as fat. For type 1 PSSM horses, these recommendations are effective.

To determine whether or not horses with type 2 PSSM should be fed like horses with type 1 PSSM, Valberg and her team queried owners of exercised Warmblood horses previously diagnosed with type 2 PSSM and managed with the aforementioned diet in addition. They found that 80% of owners reported an improvement in their horses’ performance; however, more than half (53%) were still not performing at the expected level.

“Even though many owners were not completely satisfied with their horse’s ability to move forward and collect, the researchers indicated the current diet and exercise recommendations for horses with type 1 PSSM will help horses with type 2 PSSM. Unfortunately, those recommendations do not eliminate performance issues completely, and additional research is needed,” summarized Petroski-Rose.

Re-Leve is a high-calorie, low-starch concentrate suitable for many performance horses with PSSM. For more information on Re-Leve and additional recommendations regarding high-fat, low-starch diet for horses with PSSM, consult a Kentucky Equine Research nutrition advisor today!

*Williams, Z.J., M. Bertels, and S.J. Valberg. 2018. Muscle glycogen concentrations and response to diet and exercise regimes in Warmblood horses with type 2 polysaccharide storage myopathy. PLoS One. 13(9):e0203467.