Pet Keen is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

PSSM in Horses: What It Is, Symptoms & Treatment

horse knee close up

When you own horses, it’s absolutely essential that you learn frequently seen health issues to stay on top of things. Sometimes, our horses encounter problems that require medical attention and evaluation.

Polysaccharide storage myopathy, or PSSM, is a muscular disease that affects certain breeds over others. Because of its nature, it’s essential to gain knowledge about exactly what it can cause and how to manage it. Let’s find out more!


What Is PSSM?

PSSM is a muscular disease that causes an abnormal amount of glycogen, or sugar, to collect in the muscles. The word polysaccharide breaks down to ‘poly’ meaning ‘many’—and ‘saccharide,’ meaning ‘complex sugars.’  Myopathy refers to muscular complications.

So, it breaks down as an unusual amount of complex sugars in the muscles. So, why is that complicated? Because it completely disrupts the muscle function, causing performance issues.

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

What Are the Symptoms of PSSM?

  • Sweating
  • Lameness
  • Sensitive muscles
  • Muscle tremors
  • Lameness
  • Change in behavior

Horses suffering from PSSM might develop one or all of the related symptoms.

Is PSSM Curable?

There is no known cure for PSSM, but the symptoms are manageable through treatment, exercise, and diet.

Is PSSM Preventable?

Unfortunately, since PSSM is genetic, horses receive the defect from their parents. The only real way to prevent PSSM is to avoid breeding a horse diagnosed with PSSM-1. PSSM-2 hasn’t revealed a direct cause, but breeding is still ill-advised.


How Do You Manage Horses with PSSM?

Even though horses will always have PSSM no matter the treatment, you can manage symptoms to soothe their condition. Tailoring a diet precisely to fit their needs is essential, which can be at the supervision of your vet.

You can also help to manage the condition with exercise. Physical therapy with a professional is sometimes necessary, so that is another avenue of care.

Dietary Care for PSSM Horses

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

Adding in magnesium and acetyl-L carnitine help with muscle relaxation and glucose tolerance.

Since the symptoms can vary from horse to horse, working with an equine nutritionist can help you determine exactly what to feed, how much, and what to use for additional supplementation.

horse eating
Image Credit: hortensia, Pixabay

Exercise for PSSM Horses

Even though there is much more glycogen in a PSSM-positive horse, they can experience energy deficits when they exercise. So, diet is the primary focus, while exercise is tailored to fit the horse’s needs.

Movement allows your horse to utilize the glycogen in their bodies, so the more they use their muscles—the better. It enhances mobility, metabolism—and prevents tying up.

Even though you can safely perform an exercise at home with your horse, sometimes professionals need to step in to help. Some horses with PSSM require physical therapy on a routine schedule to strengthen their gait and increase proper muscular function.

PSSM-1 vs. PSSM-2

You might have heard that there are two variants of polysaccharide storage myopathy. PSSM-1 genetically passes through the bloodline, caused by the GYS1 mutation.

PSSM-2 has no link to the GYS1 mutation and is, therefore, an anomaly for science at this time.

How Is PSSM Diagnosed?

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

PSSM-2 doesn’t have a surefire cause, but it is diagnosed through a muscle biopsy. If glycogen is clumped into the muscle fiber and cell membranes, these horses would be PSSM-2 positive.

Is a Particular Horse Breed Susceptible to PSSM?

Even though all it takes are the right genetics to contract PSSM, it is prevalent in certain breeds.

Some breeds include:

Many large draft horses suffer from this condition as well.

Image Credit: Picsoftheday, Shutterstock

Can Other Disorders Mimic PSSM?

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

Is PSSM Expensive to Treat?

As with any other medical condition, PSSM can be expensive to treat. Because it is lifelong, it presents a repeating cost. There is no way to determine just how expensive it is since the severity varies from horse to horse. It will depend on the treatment or elective therapies you use to combat the issue.

Horses with mild PSSM might be totally manageable with diet and exercise alone, making the disease inexpensive to treat. However, horses with extreme tying up might require professional intervention.

Work diligently with your veterinarian to determine a care plan for your horse. Understanding the therapeutic requirements can put into perspective how much out-of-pocket expense you will incur.


Wrapping Up

Even though PSSM is a lifelong problem, it doesn’t have to be debilitating. With a proper care plan, these horses can live semi-normal lives with few complications.

Any horse who has PSSM-1 or PSSM-2 should be entirely out of any breeding program. Passing along these genetics leads to a whirlwind of continuing trouble for future generations. We must work hard to phase out PSSM horses by preventing the genetic condition from genetically transmitting.

Featured Image Credit: Picsoftheday, Shutterstock

Our vets

Want to talk to a vet online?

Whether you have concerns about your dog, cat, or other pet, trained vets have the answers!

Our vets