PSSM in Horses: What Is It, Symptoms, Can It Be Cured?

When you own a horse, it is very important that you learn about the health problems that are often seen in order to stay on top of everything. Occasionally, our horses experience problems that require medical attention and evaluation.

Polysaccharide storage myopathy, or PSSM, is a muscle disease that affects certain breeds more than others. Due to its nature, it is important to gain knowledge of what can cause it and how to manage it. Let’s find out more!

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What is PSSM?

PSSM is a muscle disease that causes abnormal amounts of glycogen, or sugar, to build up in the muscles. The word polysaccharide breaks down into ‘poly’ which means ‘many’—and ‘saccharides’, which means ‘complex sugar’. Myopathy refers to muscle complications.

So, it breaks down as unusual amounts of complex sugars in the muscles. So, why is it complicated? Because it actually interferes with muscle function, causing performance problems.

Not all horses will exhibit the same severity of disease. Some will show signs of low to moderate, while others will have extreme cases that can lead to inequality.

What are the Symptoms of PSSM?


  • sweating

  • Inequality

  • Sensitive muscles

  • muscle tremor

  • Inequality

  • Changes in behavior

Horses suffering from PSSM may experience one or all of the associated symptoms.

Is PSSM Curable?

There is no known cure for PSSM, but symptoms can be managed through medication, exercise, and diet.

Can PSSM Be Prevented?

Unfortunately, because PSSM is genetic, horses receive the defect from their parents. The only real way to prevent PSSM is to avoid breeding horses diagnosed with PSSM-1. PSSM-2 has not revealed the direct cause, but breeding is still not recommended.


How Do You Manage Horses with PSSM?

While your horse will always experience PSSM no matter what the treatment, you can manage the symptoms to calm the condition. It is very important to properly adjust the diet to suit their needs, which can be done under the supervision of your veterinarian.

You can also help manage the condition by exercising. Physical therapy with a professional is sometimes necessary, so that is another way of treatment.

Diet Care for PSSM Horses

People with PSSM require a low-starch, high-fat diet to reduce the amount of abnormal sugar in the muscles. Feed healthy amounts of fats and oils — some horses need 2 cups of oil per day while others need very little.

Added magnesium and acetyl-L carnitine aid in muscle relaxation and glucose tolerance.

Because symptoms can vary from horse to horse, working with a equine nutritionist can help you determine exactly what to feed, how much, and what to use for supplemental supplements.

horse eat

Training for PSSM Horses

Although there is more glycogen in PSSM-positive horses, they can experience an energy deficit during exercise. So, diet is the main focus, while exercise is tailored to the needs of the horse.

Movement allows your horse to use the glycogen in its body, so the more they use their muscles—the better. It increases mobility, metabolism—and prevents bonding.

While you can safely do the exercises at home with your horse, sometimes professionals need to step in to help. Some horses with PSSM require physical therapy on a regular schedule to strengthen their gait and promote proper muscle function.

PSSM-1 vs. PSSM-2

You may have heard that there are two variants of polysaccharide storage myopathy. PSSM-1 is genetically crossed lineage, caused by the GYS1 mutation.

PSSM-2 is not associated with the GYS1 mutation and is, therefore, an anomaly to current science.

How is PSSM Diagnosed?

When vets screen for PSSM, they perform blood tests or take hair samples to reveal the GYS1 variant. If the test shows a positive GYS1 result, the diagnosis is complete.

PSSM-2 has no definite cause, but is diagnosed through a muscle biopsy. If glycogen clumps into muscle fibers and cell membranes, these horses will be PSSM-2 positive.

Are Certain Horse Breeds Vulnerable to PSSM?

While all it takes is the right genetics to contract PSSM, it is common in certain breeds.

Some of the races include:

  • American Quarter Horses

  • American Paint Horse

  • Appaloosa Horse

  • original ancestry

  • Dales Pony

  • cob horse

  • Arabian Horse

Many large draft horses suffer from this condition as well.


Can Other Distractions Mimic PSSM?

Hyperkalemic periodic paralysis, or HYPP, is another genetic muscle disease that may be confused with PSSM, because they share many common symptoms. It causes muscle spasms, weakness, paralysis, and shaking in horses.

Is PSSM Expensive to Treat?

As with any medical condition, PSSM can be expensive to treat. Because it’s lifetime, it incurs recurring costs. There is no way to determine how expensive it is as the severity varies from horse to horse. It will depend on the treatment or elective therapy you are using to treat this problem.

Horses with mild PSSM may be completely controllable with diet and exercise alone, making the disease inexpensive to treat. However, horses with extreme ties may require professional intervention.

Work diligently with your veterinarian to determine a treatment plan for your horse. Understanding the therapeutic requirements can determine how much it will cost you.


PSSM: Last Thoughts

While PSSM is a lifelong problem, it doesn’t have to be debilitating. With the right treatment plan, these horses can lead a semi-normal life with few complications.

Any horse that has PSSM-1 or PSSM-2 must be completely out of the breeding program. Passing down these genetics leads to a whirlwind of ongoing problems for future generations. We must work hard to stop PSSM horses by preventing genetic conditions from genetic transmission.

Featured Image Credit: Picsofttheday, Shutterstock

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