Data on EPSM Signs in Various Breeds
by Beth A. Valentine, DVM, PhD
A lot of information has become available, published and unpublished, regarding clinical signs and percentage of horses affected by EPSM (equine polysaccharide storage myopathy). This information can be helpful to horse owners who are having trouble identifying the cause of physical or apparent behavioral problems in their horses. As is often the case with new information, this data is taking awhile to become available to veterinarians. As an informed horse owner you can help your veterinarian by discussing the possibility of EPSM if your horse has problems that fit the profile of an EPSM horse, especially if no other obvious cause can be found.

EPSM horses, including drafts, have so far been identified in the United States, Canada, England, Switzerland, Spain, France, Italy, Australia, and New Zealand. With time I expect to see this problem identified in all parts of the world where horses are. EPSM is not a new problem‹it has likely been with us for hundreds of years. But, like many medical problems in people as well as in animals, until you know what you're looking for, you aren't going to find it.

A summary of findings in 250 horses diagnosed as having EPSM was published in the December 1, 2001 Journal of the American Veterinary Medical Association. It is important to note that many horses had more than one of the following clinical problems.
  • Gait abnormality (including stiff gait, difficulty cantering, odd hind limb action, stifle problems, but not including shivers): 129 horses—91 were Quarterhorse, draft, or warmblood related, 38 were other breeds. Of these horses, 118, or 92%, responded to diet change.

  • Tying up: 90 horses—48 were Quarterhorse, draft, or warmblood related, 42 were other breeds; 84, or 93%, responded to diet change.

  • Lack of energy and/or poor performance: 73 horses—54 were Quarterhorse, draft, or warmblood related, 19 were other breeds; 68, or 93%, responded to diet change.

  • Muscle loss or poor muscling: 64 horses—51 were Quarterhorse, draft, or warmblood related, 13 were other breeds; 56, or 88%, responded to diet change.

  • Severe generalized weakness (these horses had difficulty standing up after lying down): 22 horses—19 were Quarterhorse, draft, or warmblood related (mostly drafts), 3 were other breeds; 12, or 54%, responded to diet change.

  • Shivers: 21 horses—17 were Quarterhorse, draft, or warmblood related (mostly drafts and warmbloods), 18, or 86%, responded to diet change.

  • Behavior problems in harness or under saddle: 18 horses—9 were Quarterhorse, draft, or warmblood related, 9 were other breeds; 16, or 89%, responded to diet change.

  • Back pain or total body pain: 15 horses—10 were Quarterhorse, draft, or warmblood related, 5 were other breeds; 14, or 93%, responded to diet change.

  • Difficulty with trimming hooves or shoeing: 12 horses—11 were Quarterhorse, draft, or warmblood related, 1 was another breed; 11, or 92%, responded to diet change.

  • Weakness in the hind limbs: 11 horses—10 were Quarterhorse, draft, or warmblood related, 1 was another breed; 10, or 91%, responded to diet change.

  • Episodic colic: 6 horses—5 were Quarterhorse, draft or warmblood related, 1 was another breed; 6, or 100%, responded to diet change.

Although some of the warmbloods tied up, most of them had gait abnormalities, hind leg weakness, attitude/training problems, back soreness, or shivers. Drafts are also less likely to have obvious tying up problems. Hind limb gait abnormalities, including stiff gait and shivers (often misdiagnosed as stringhalt), and overall muscle wasting and weakness are the most common problems in drafts. The most devastating problem, seen almost exclusively in drafts, is a sudden development of severe muscle weakness or damage, such that the horse is unable to rise. This condition constitutes a crisis, as only about 50% of these horses survive following diet change.

In another study, presented at the December 2002 meeting of the American College of Veterinary Pathologists (the abstract of which is published in Veterinary Pathology), 36% of all non-draft horses had evidence of the type of metabolism that leads to EPSM when samples of muscles were examined. Studies continue to confirm previously published incidence rates of 66% in draft-related horses, meaning that about two of every three drafts have the type of metabolic difference that can lead to signs of EPSM. Given this high rate of incidence, and given that EPSM horses often have the best build, best performance, and best temperament, I can't help wondering if we haven't somehow selected for this type of metabolism as we selected for horses with increased muscling and performance potential. If so, it's about time we figured out how to feed them right.

It seems to me that many problems in drafts, such as hind limb stiffness, overall muscle wasting, low energy, shivers, and sudden death have been explained away as part of being a draft horse. I don't believe this is true. Rather, I find that healthy drafts can live long and productive lives. The draft mentality of working without complaining likely helps keep many EPSM drafts going without showing obvious signs of a problem until the situation is severe, at which point it might be too late for a reversal.

When you look at how carefully human athletes tailor their diets to enhance their performance, it's incredible that we aren't nearly as conscientious about equine diets. But then, until recently we didn't know enough about the best diet for athletic performance in horses. For equine athletes in many disciplines—including farming, logging, and pulling—the EPSM-type diet is ideal. Even for non-EPSM horses it is the best diet for muscle function, not to mention the horse's comfort.


return to Signs of EPSM in Draft Horses

Beth A. Valentine, DVM, PhD, is a veterinary pathologist at Oregon State University in Corvallis and the author of Draft Horses, an Owner's Manual. This article appeared in The Evener 2003 issue of Rural Heritage.

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26 October 2011 last revision