Last Updated on March 11, 2022 by Allison Price

Horses with muscular disorders are a common cause for disability and poor performance. Polysaccharide storagemyopathy (PSSM), is a common cause of recurrent episodes in muscle disease. It affects Quarter Horses and Paint Horses . PSSM is also less common in drafts, draft crossbreeds and warmbloods.

PSSM is widely recognized as a cause of exertional (ER-muscle loss with exercise) in horses. muscle cramping and tying up is the primary sign of this condition. Most often, the signs include muscle stiffness, excessive sweating, skin twitching and profuse sweating. Horses most commonly show these signs after they have been put in their initial training, or after they have had very little exercise. The episodes usually start after a very brief amount of exercise, such as walking or trotting for 10-20 minutes. PSSM symptoms can also be seen in horses who do not exercise. Horses with PSSM can become lazy, have a shifting lameness and tremors in the flank area. Horses may urinate when they stop moving. After exercise, some horses may try to pawe and roll.


The clinical signs of this condition may be different for different breeds or severity. Many horses with PSSM experience muscle stiffness in the beginning of their training. However, horses that are mildly affected may only have one to two episodes per year. Muscle pain and stiffness can cause horses to be unable or uncomfortable to stand, and even when they are lying down.

PSSM is primarily a Glycogen Storage Disorder. Normal tissue has insulin which drives glucose from blood into the muscle and liver cells. This glycogen is then used later as energy. PSSM is an abnormal accumulation of glucose in muscle. In normal tissue, insulin drives glucose from the blood into muscle and liver cells to be stored as glycogen and later used as energy. These horses’ urine is often colored coffee (myoglobinuria). This is due to the release of muscle proteins into the bloodstream. If the horse becomes dehydrated, this is a very serious problem.

The results of traditional complementary tests such as urinalysis and measurement of muscle enzymes are not usually very helpful in diagnosing PSSM. However, muscle biopsy is an important tool. In 1992, the first description of PSSM was based on the presence of amylase resistant polysaccharide from skeletal muscle biopsies. As diagnostic features, aggregates were later added. These amylase-sensitive muscle glycogen lakes and subsarcolemmal muscles glycogen lakes were also added.

Two types of PSSM disorders have been identified by genetic research. PSSM1 is caused by a mutation in the glycogen synthase genes ( YS). PSSM2 affects horses with abnormal histologic muscle glycogen, but does not cause the GYS1 gene mutation. It is not known what the genetic basis of PSSM2 may be. PSSM1 horses and PSSM2 horses have similar clinical signs.

Exercise and diet are important in improving the condition of horses. The goal is tostabilize blood glucose, insulin, and provide regular exercise that increases glycogen metabolism. No matter how severe the score for abnormal polysaccharide found in muscle biopsy specimens is, it has been proven that both exercise and diet can improve symptoms.

Because horses with PSSM have Therefore,recommendations include a diet that provides < 12% of digestible energy (DE) as non-structural carbohydrate (NSC), 15-25% of DE as fat and fermentable fibre, and regular daily exercise. This diet produces a low insulinaemic and glycaemic response and provides an alternative energy source in the form plasma-free and volatile fatty acid.

PSSM horses should be analyzed for their forage. Because of the insulinaemic and glycaemic responses that hay that contains more than 17% of DE may be poor for horses with PSSM. However, horses with a NSC content below 12% do not seem to experience the same post-prandial insulinemic or glycaemic response as horses with PSSM. The total daily caloric needs and the need to provide calories in the form fat without causing excessive weight gain may determine the importance of limiting NSC content in hay.

Horses that have not been fed concentrates may still get symptoms from grass, which can potentially contain high levels of sugar. A well-maintained pasture should have low-sugar grasses, and few legumes like clover, alfalfa, or lucerne. Although hay that is mature should be preferred over hay that is less energy-dense and immature, all hay should be free from mold, dust and other foreign material. High levels of watersoluble carbohydrates (WSC) have been linked to insulin resistance and PSSM. Therefore, hay that contains these WSCs should be soaked in water . For reducing WSC content, soak hay in water for either 30 minutes or 60 minutes. Other factors that can trigger ER include dust, mold (mycotoxins), and chemicals sprayed onto the hay.

Numerous studies have shown that giving sweet or other starch-based concentrated feeds to PSSM horses can increase exercise intolerance and cause muscle pain in PSSM. Specific triggers include soy, wheat and molasses. The common recommendation is to eliminate all grains, sweet feed and molasses from your diet and replace them with high-quality forages like alfalfa or grass-alfalfa hybrid hay diets. Oat hay should not be used as grain hay. High-starch kernels of high-starch grains can stick to the stems and increase the starch content. To provide additional energy, fat is often added to the diet. Supplements of vegetable oil, animal fats, or other energy sources like fermentable beet pulp, can be added to the diet to provide an alternative source of energy. Flaxseed oil, fish oil, and flaxseed oil have a higher omega-3:omega-6 ratio than corn oil. However, they are more susceptible to oxidation and can easily go rancid at room temperatures. Cold-pressed coconut oil is a better choice for horses who are experiencing symptoms like ‘typing up’. It has a higher omega-3:omega-6 ratio than fish oil and flaxseed oil. However, these oils can easily go rancid at room temperature. To prevent oxidation, these feeds must be kept in cool and dry places. These fats could increase the production of free radicals if they are added to the diet. PSSM horses should be given a vitaminE supplement to prevent cellular oxidation caused by free radicals.

It is not always possible to reduce the severity of the condition by improving horse feeding. Regular exercise is recommended. If there are no signs of CK increases, the horse should be waited for at least 15 minutes each day. The workload can then be increased gradually if necessary. Active riding can begin when the horse is able to be worked for at least 30 minutes without difficulty.

Bovine colostrum (BC), a powerful ingredient that is rich in protein, can be added to the horses with PSSM. It is also a good source of nutrition. It has been shown to be a nutritional supplement that can improve muscle mass, musculoskeletal growth and repair, and muscle recovery. Horses with PSSM can experience muscle loss after exercise. BC supplementation may help to improve muscle recovery and mass. BC supplementation also has a positive impact on blood glucose control. This is especially important for horses with PSSM, whose primary goal is to maintain blood sugar levels.

Reishi, which is a Ganoderma Lucidum mushroom found in Immubiome Lean Muscle can be added to horse’s PSSM diet. Reishi supplementation has been proven to help control sugar. The numerous bioactive compounds such as polysaccharides and triterpenoids that can be extracted form the fruiting bodies, cultured mycelia, and spores, have been shown to help with the recovery of muscle wear.

Numerous studies have highlighted the important link between gut bacteria, skeletal muscles metabolism and glucose homeostasis for animals. Also found in Immubiome Lean Muscle. SCFA (short chain fatty acids) are an important source of energy in the colon. They are mostly produced by bacteria fermentation of undigested carbohydrates from the horse’s hindgut. SCFA are signalling molecules that play a role in the regulation of insulin and systemic lipid metabolism. Probiotics can positively impact dietary protein digestion, utilization in the digestive tract, helping the horse athlete better assimilate proteins from its diet to build lean muscle . The production and consumption of energy from diets are also affected by gut microbiota. Supplementing horses’ diets with probiotics can reduce some symptoms of PSSM. This includes glucose homeostasis, muscle mass, and strength.

Modifying dietary components is a key strategy to manage muscle disorders in horses. PSSM is also a management issue. Horse owners should be aware that the recommendations for PSSM are to reduce muscle glycogen synthesis, promote oxidative metabolism, and provide fat as an alternative fuel. This is not all that can be done. Horse owners should supplement their diet with probiotics, Reishi, bovine colostrum and other beneficial ingredients to positively influence carbohydrate metabolism and establish glucose homeostasis.

Allison Price
Allison Price

I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!