|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A lot of information has become available, published and unpublished, regarding clinical signs and percentage of horses affected by EPSM (equine polysaccharide storage myopathy).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 problemit 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.
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 disciplinesincluding farming, logging, and pullingthe 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.
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