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What is EPSM?

Equine Polysaccharide Storage Myopathy (EPSM) is “a muscle condition that results in an excessive buildup of glycogen in the muscle. In the normal horse, glycogen is the energy source in muscle contraction. An EPSM horse cannot complete this process, resulting in an excess in stored glycogen.”¹ This eventually leads to muscle cramps and weakness. While most breeds of horses are susceptible to this disease, EPSM is particularly common in draft horse breeds.²

What are the symptoms of EPSM?

Symptoms include tying up, reluctance to move, stiff gaits especially in the hindquarters, and sweating. Some horses also display reluctance to trot, back or canter, muscle atrophy and weakness, or lack of energy.³

EPSM is sometimes confused for:

Back or hock soreness

Colic

Equine Protozoal Myeloencephalitis (EPM)

Equine Motor Neuron Disease (EMND)

Lyme Disease

Anemia

Tying-Up

Can EPSM be treated?

Horses with EPSM can be managed through diet therapy. “Horses with this disease are not able to derive adequate muscle energy from carbohydrates, the main source of energy in grains, sweet feeds, and pelleted horse feeds. The diet therapy involves decreasing the amount of dietary carbohydrates, and replacing them with fat as an energy source.” There are many ways to add fat to a horse's diet, including vegetable oil, powdered animal fat, and commercial feeds and supplements designed to be high in fat. For best results, dietary therapy should be administered during the early stages of the disease. Also, keep in mind that it may take as long as four months for diet therapy to be effective.⁴

Diet Therapy⁵ includes:

• Forage
• Either grass or legume (alfalfa) hay
• Vitamins & Minerals
• Vitamin E (at least 1 IU Vitamin E per lb of horse)
• Selenium (1-2mg per 1000lbs of horse per day where deficient)
• General vitamins & minerals (optional depending on forage quality)
• Fat source
• Equivalent to 1lb of fat/1000lb horse
• When using oil, 2 cups = 1lb
• Can also use 100% fat supplements
• Treats like carrots and apples (in moderation)

It is also critical that horses with EPSM get as much daily turnout and as much regular work as possible. Without exercise, a horse is not able to utilize the dietary fat they are getting.

Can my other horses be on the diet as well?

Previous research done by Dr. Harold (Skip) Hintz at Cornell University and Dr. David Kronfeld at Virginia-Maryland Veterinary College has shown no adverse effects when this diet was used on healthy horses.⁶

How can I detect EPSM?

Affected horses may appear completely normal for many years. At this time, diagnosis is best made by examining a muscle biopsy for the characteristic changes.⁷ This procedure is fairly simple and usually can be preformed at by your veterinarian at your barn. Contact your local veterinarian for cost and details.