EPSM: How Diet Can Effect Performance

EPSM (Equine polysaccharide storage myopathy) has been shown to be the major cause of a common muscle disorder of horses, known as exertional rhabdomyolysis or “tying up.” Beth Valentine, DVM, PhD, Dipl ACVP, the foremost researcher and expert on EPSM, proposed the first successful therapy to halt and reverse the progression of EPSM. A graduate of the NY State College of Veterinary Medicine at Cornell University, Dr. Valentine is currently a professor at OSU College of Veterinary medicine.

Dr. Valentine reports, “I am a veterinary anatomic pathologist, in the Veterinary Diagnostic Laboratory, involved with many different species and pathologic disorders. I have a special interest in equine disease and in neuromuscular disease. I head the Neuromuscular Disease Laboratory, which is currently involved in the study of the incidence, pathologic features, and pathogenesis of equine polysaccharide storage myopathy. The laboratory has also been involved in collaborative studies within and outside of the College of Veterinary Medicine.”
SymptomsHorses with EPSM lack the ability to obtain or properly utilize energy from soluble carbohydrates, which are the main source of energy in grains, sweet feeds, and pelleted horse feeds. The exact pathogenesis of EPSM is still not known, although pathologic findings of abnormal polysaccharide storage and response to diet change suggest abnormal metabolism of starch and sugar.
Glycogen is on of the energy sources for muscle contraction. An EPSM horse has an excessive buildup of glycogen in the muscle resulting in muscle cramps and weakness. Obvious symptoms include tying up, reluctance or inability to move, stiff gaits especially in the hindquarters, and sweating. Less obvious signs of EPSM are reluctance to transition into gaits (from walk to trot / trot to canter) difficulty backing up, muscle atrophy and weakness, or lack of energy. This condition can be misdiagnosed as back or hock soreness or colic.

Two other conditions that may be related to EPSM, are “Stringhalt” and “Shivers.” Some cases of both have been successfully treated with Dr. Valentine’s EPSM diet. The first is “Stringhalt" identified by abnormal hind leg action, particularly when the horse backs or turns. It is often? described as a "hitch" or "cramp" in which the horse pauses with its hind leg in the air before stomping it down. It can also happen while standing, or on the first step as they get going, or on the last step before stopping. It can effect one or both hind limbs. It is thought to be caused by a problem with the nerve supply to the hind leg muscle, but those horses that respond to an EPSM diet likely have muscle cramps rather than nerve problems. The second condition is"Shivers". This is a condition that appears similar to stringhalt. It usually happens only at a standstill. One classic symptom is that the horse abnormally elevates its tail and has a lack of energy to the hind limb muscles. Horses with Shivers typically have difficulty with lifting hind legs while being shod - it’s often only one back leg that shows symptoms. They may develop more severe signs such as muscle wasting and weakness over a period of time.
DiagnosisWhile EPSM is a relatively newly recognized disease it is believed to have been around for hundreds of years. It has been confirmed or suspected in virtually every draft horse breed, although it is not breed specific as it has been identified in numerous other breeds, Thoroughbreds being one of them. PSSM (Polysaccharide Storage Myopathy) also referred to as Exertional Rhabdomyolysis is a separate glycogen storage disorder found in Quarter Horses, Appaloosas, and paints. Although, I have yet to find data indicating any difference between the symptoms or treatment. These are thought to be the same thing now – the only controversy left is whether TBs that tie up have RER or EPSM. PSSM is the acronym Minnesota uses, I use EPSM, and more recently I have take to using EPSSM to try to bridge the gap and avoid confusion.

A positive response to diet change is usually accepted as evidence that your horse has EPSM. The best diagnostic test is a muscle biopsy, which generally runs $200 and is fairly non-invasive. It is a faster way to rule out or identify the problem.
Treatment - diet vs. drugsRace horses who do not have a clinical case of EPSM may experience “tying up” for other reasons due to the nature of their work. Of interest it the fact that furosemide (Lasix) has been shown to decrease serum levels of potassium, which can predispose muscle to injury during exercise.
Banamine is used routinely to treat an episode of tying up. Some trainers take preventative measures by adding Vit E and Selinium to their diet. A routine of putting the horse on a walker after a work or race to keep them moving is also beneficial. There are no clinical studies on whether an EPSM diet may reduce the number of tying up incidents in race horses, but Dr. Valentine has worked with many racing TBs that have tying up problems, and all that she knows of have responded well to a change to an EPSM diet. This observation certainly warrants further research. Coincidentally, many race horses are already following Dr. Valentine’s diet unknowingly.
If your horse does have EPSM, the treatment is dietary manipulation to provide a high fat, high fiber, low starch and sugar diet. Cereal grains (oats, corn, and barley) are typically the major source of starch and sugar in a horse’s diet. In EPSM horses, energy must be provided by other sources, including extra fiber (such as Beet Pulp), fatty acids from fats or oils (liquid corn oil), and amino acids from protein (such as alfalfa). Dr. Valentine recommends gradual increase in dietary fat aiming for at least 1 pound of fat (2 cups oil or equivalent in other fat source or sources) per 1000 pounds of horse per day, along with as much reduction in starch and sugar as possible. As much turnout time and regular exercise as possible are also important. This therapy has proven to successfully control signs of muscle dysfunction in most affected horses. Owners should realize that it will take about 4 months for their horses to fully fat adapt, and tie ups or other muscle problems can still occur during this time. Additional supplements such as more significant amounts of chromium and magnesium may also be useful in some cases.
On a personal note, I have experienced success with Dr. Valentine’s EPSM diet on several occasions. I currently have a warmblood/Thoroughbred mare who came to Second Chance Ranch with a mysterious lameness that could not be positively diagnosed for years. The previous owner had exhausted all diagnostic efforts, including MRI, Ultrasound, X-rays and repeated flexion tests. I was told she had a problem with her right hind suspensory. I first noticed that the mare improved with work, and the stiffness to the right appeared, in my opinion, to actually come from the stifle or possibly higher up in the Gluteal region. The mare did not have any of the clearly obvious signs of EPSM, however, she did have an unexplained muscle weakness and stiffness. I put her on Dr. Valentine’s EPSM diet and saw progressive improvement - she is currently sound and working 3nd level dressage.
Dr. Valentine generously shares her time and knowledge on a discussion board hosted by Rural Heritage; http://dfelten.tempdomainname.com/messageboard/virtualvet/
She can also be reached at;Beth A. ValentineOregon State UniversityCorvallis, OR Phone: 541 737 3261Fax: 541 737 6817mailto:Beth.Valentine@oregonstate.edu

Reference materials;

(Dr. Valentine’s bio, definition of disease and symptoms)http://oregonstate.edu/vetmed/biomed/valentine.htm http://www.draftresource.com/EPSM/Draft_EPSM_Report.html

Other research articles http://equisearch.com/horses_care/health/illnesses_injuries/EPSM110503/
http://www.thehorse.com/ViewArticle.aspx?ID=9795&kw=epsm
http://www.ruralheritage.com/vet_clinic/epsm_biopsy.htm