Case Histories


PSSM and A Quarter Horse Named Doc

By Claire C. Cox-Wilson

Doc...happy and sassy now that his PSSM is managed with a proper diet and regular exercise

One morning in November of last year, my husband David noticed Doc lying down in the back pasture. We watched him get up, take a couple of steps, turn around and lie down again. The other three horses were peacefully grazing close by. David turned to me and said, “He’s not right. He’s just--- not right.” This was not normal behavior for our horse.
We walked down to the pasture together. Doc didn’t move. When he finally did get up, I noticed his hindquarters seemed extremely stiff. Doc made it very clear he did not want to be touched. His golden eyes were sad and clearly said---“Just leave me alone.”
Doc, our beloved buckskin Quarter Horse had been suffering for years and yet we never managed to recognize the signs and symptoms of Polysaccharide Storage Myopathy (PSSM).

The Quest for a Diagnosis
We all deal with our troubles differently. David sank into depression. I went into manic research mode.

  • I knew from experience that muscle pain and soreness could be a result of lameness compensation.
  • We pursued the lameness issue and found arthritis and pastern ringbone in both front legs. Joint injections with Hyaluronic Acid (HA) and Triamcinolone gave Doc almost immediate relief.
  • However, his hind-end stiffness persisted.
  • Research shows that muscle soreness can be caused by mineral imbalances. We immediately ruled this out because for years we had been having our hay analyzed and mineral balanced by Dr. Eleanor Kellon.
  • A thyroid panel eliminated a low functioning thyroid as a cause for exercise intolerance and tying up.
  • Because of Doc’s bloodlines, Hyperkalemic Periodic Paralysis (HYPP) was another consideration. The symptoms of this disease can be similar to those of PSSM. A call to the AQHA ruled out that possibility.
  • After reading an article about a Morgan with PSSM, it finally all came together for me. Doc had, at one time or another, displayed all the symptoms in that article.
  • Clearly the next step was a muscle biopsy, the only accurate test for PSSM.

A week later, we received the results of Doc’s muscle biopsy. Our beloved Doc had PSSM.

What is PSSM?
Dr. Eleanor Kellon of Equine Nutritional Solutions defines PSSM as a problem with energy generation within the muscle cell that is characterized by the muscle storing large amounts of glycogen (storage form of glucose) and an abnormal form of carbohydrate as well. Deposits of fat in the muscle are lower than normal. Studies have found that these muscles metabolize carbohydrate normally so the high levels of carbohydrate storage don't occur because of a problem with burning them. Researchers still haven’t found what the metabolic problem inside PSSM muscle cells is, why they preferentially store large carbohydrate reserves, or why supplying additional fat helps. It may be that the extra fat "trains" the muscle to use more fat than it is inclined to do. This is beneficial because ounce per ounce fat yields more energy for the cell.
Classic Symptoms of PSSM
Horses with PSSM typically have signs of tying-up. Some horses will show signs of pawing and rolling immediately after exercise. Most horses with PSSM have a history of numerous episodes of muscle stiffness beginning with the commencement of training; however, mildly affected horses may have only one or two episodes/year.

Depending on the severity of involvement, symptoms can include any of the following:
• all around stiffness
• difficulty rising
• reluctance to “move out”
• tires easily
• saddle issues (sore back)
• bucking
• resistance to holding up the hind feet
• subtle lameness episodes
• abnormal gaits
• cranky attitude
• muscle tremors or sensitivity
• kicking at flies that aren’t there (muscle cramps)
• excessive tail swishing (muscle pain)
• looking at belly or flanks as if colicky (muscle pain)
• having a preference for rubbing or rolling a lot, or in some cases the opposite with resistance to brushing/grooming, especially over the back and rump
• affected horses may show a stiff, tense gait
• symptoms of “shivers” - abnormal hind leg action and muscle quivering; this has been described in draft breeds

If left unmanaged, over time, the muscles can atrophy and the horse can show severe muscle wasting.

Managing Doc’s PSSM
Management of PSSM mainly consists of a low carbohydrate, high fat diet, as well as regular exercise. The recommendation was one pound of fat per 1000 lbs of horse per day, which if using straight oil would mean two cups of oil for a 1000 lb horse. The consensus was that any type of oil was acceptable. I spoke with two horse owners who had followed the oil recommendations. Both of these horses had laminitis and were displaying symptoms of insulin resistance. The more I researched this disease, the more concerned I became. I was not willing to risk Doc coming down with laminitis and/or insulin resistance.

I turned to Dr. Eleanor Kellon, our long time nutritional consultant. Dr. Kellon explained that adding fat to a horse’s diet seems simple enough, however a horse’s natural diet of fresh grass is very low in fat, and the only actual “requirement” they have is for fatty acids they cannot manufacture themselves, the omega-3 and omega-6 fatty acids. These are referred to as the Essential Fatty Acids (EFAs). If we were going to supplement fat, we had to do it in as healthful a way as possible and make sure we were feeding Doc “good” fats.

Oils you buy on a store shelf and oils added to feeds, weight gain products, and fat-added rice brans are all stabilized by processes that destroy the fragile EFAs. Stabilization can also change the structure of fats, producing hydrogenated or partially hydrogenated forms, and trans fats. Stabilized/trans fats have been recognized as a health risk in Europe for decades (including in relation to heart disease, diabetes/IR), and the FDA is finally getting around to requiring label information on human foods. Ground stabilized flax, on the other hand, is produced by a low heat process, which preserves the EFAs.
Dr. Kellon suggested unprocessed/raw oil, either cocosoya or straight coconut oil. Coconut oil and cocosoya (a blend of coconut and soy oils) are highly palatable and coconut oil is high in medium chain triglycerides (MCTs), a form of saturated fat. This isn’t the same as other forms of saturated fat that people are instructed to avoid (i.e. trans-fats, hydrogenated and processed oils, or meats). MCTs are different because they can be utilized directly as energy sources by the cells---at least the cells of other mammals. Unfortunately, no equine specific data is available on this subject. However, Dr. Kellon’s diet made perfect sense to me. We would balance the high omega-6 fatty acids in these oils with ground flax, an excellent source of omega-3s.

In addition, we started Doc on L-Carnitine. L-Carnitine is made in the body from the amino acids lysine and methionine, and is needed to release energy from fat. It transports fatty acids into mitochondria, the powerhouses of cells, "furnaces" where these fuels are burned. With the exception of medium chain triglycerides such as those found in high concentration in coconut oil, all fatty acids require L-Carnitine to carry them into the mitochondria. The idea was to give Doc both a supply of the MCTs and supplemental L-Carnitine to help him utilize other fatty acids so that we could achieve the desired results with a minimal amount of actual oil.

Today, Doc's daily diet consists of free-choice Bermuda hay, about 1/2 pound of rinsed and soaked beet pulp, and a pound and a half of alfalfa/Bermuda pellets. He also gets 2000 IU of vitamin E, a cup of stabilized flax, two ounces of rice bran, and 1-2 ounces of iodized salt. In addition to the custom mineral mix specifically prepared for our Bermuda hay, Doc receives extra magnesium oxide as well. Doc's PSSM symptoms are totally controlled with less than 1/2 cup of a coconut oil and cocosoya oil combination, plus Dr. Kellon's recommended dose of L-Carnitine based on Doc's specific needs.

Doc is either longed or ridden five times a week. His gaits and transitions are smoother than ever before and he picks up both leads equally well and consistently. His attitude has changed too. Well…let’s say that now, Doc is only grumpy when the pastures are closed off for irrigation.fin


About the author:
Claire Cox-Wilson has rehabilitated her gelding Doc from Navicular syndrome and kept at bay his symptoms of PSSM.
Cox-Wilson has also kept her 30-year-old mare Tamera, going strong, in spite of Cushings disease and Insulin Resistance.
Claire retired in 2002 from a nursing career that spanned 32 years.
Now, she cares for her animals, makes custom horse hair dreamcatchers and sells herbal mixes for horses. She can be contacted through her home website at or her business website

About Eleanor Kellon, VMD:
Eleanor Kellon (Equine Nutritional Solutions, Ephrata, Pennsylvania) is an expert in the field of equine nutrition as well as matters concerning performance horses. Dr. Kellon is veterinary editor for the Horse Journal and John Lyons Perfect Horse magazines. Equine Cushings and Insulin Resistance are just two of her many areas of expertise. Dr. Kellon can be reached for private consultations by e-mail, at


PSSM....Could my horse have it? by Karen J. Wolfsheimer, DVM, PhD

Quarter Horses Have Particular Muscular Worries; Horse Journal, June 2006, Vol.13, No.6