EPSM—Muscle Disease in Draft Horses
by Beth A. Valentine, DVM, PhD
The muscle disease Equine Polysaccharide Storage Myopathy (EPSM) has been confirmed or suspected in virtually every draft horse breed, including Belgian, Percheron, Clydesdale, Shire, Haflinger, Norwegian Fjord, Irish Draught, Friesian, Gypsy Vanner, draft cross, and a draft mule. This newly-recognized disease, under research at the College of Veterinary Medicine at Oregon State University, has likely been around for hundreds of years. It has been identified in many breeds of horse, but appears to be particularly common, severe, and difficult to detect in the draft breeds. In fact, approximately two-thirds of all draft related horses show evidence of EPSM, if you look at their muscles microscopically.
In drafts EPSM has been identified as a cause of severe muscle wasting and weakness in both young and older horses, of "tying up" (Monday Morning Disease) in older horses, as a cause of poor performance, "shivers," and other abnormal hind limb gaits. Affected horses may easily be misdiagnosed as having foaling complications, colic, or other diseases. Most devastating of all, this disease has been identified as causing recumbency ("down horses") due to weakness during work, associated with foaling, at rest, or following general anesthesia.
EPSM and Other Conditions
"Monday morning disease" is most often described in hard-working draft horses that are given a day off with full grain feed. When they are asked to work the next day, these horses show severe signs of the condition known as "tying up" in saddle horses—muscles become stiff and begin to degenerate; the horse stops moving and may go down.
Massive muscle injury results in release of the pigment myoglobin from damaged muscle, and the urine becomes a dark red-brown (myoglobinuria). Because of this reddish color, the disease is also called "azoturia" ("azo" from the red clothing dye + "t" from who knows where + "uria," referring to urine). Other names include "set fast," "exertional myopathy," and "exertional rhabdomyolysis."
We believe the massive muscle damage in EPSM drafts is due to lack of muscle energy. The common occurrence of slightly increased levels of muscle enzymes in the blood of apparently normal or only mildly affected horses suggests that these horses have low-level muscle injury during exercise. We don't yet understand what puts them over the edge into massive muscle injury, but studies of muscle from horses with signs of Monday morning disease show that EPSM is a common underlying condition, and we believe EPSM is the cause of the disease. Whether or not all horses with Monday morning disease also have EPSM remains to be absolutely proven, but so far evidence suggests they do.
"Stringhalt" (sometimes called "springhalt") is a condition producing abnormal hind leg action, especially when the horse backs or turns. Some people describe this action as a "hitch" or "cramp" in which the horse pauses with its hind leg in the air before stomping it down. It occurs most often when the horse backs or turns in a tight circle, but I have seen horses do it while standing, or on the first step when they get going, or on the last step before stopping. In many cases, horses thought to have "stringhalt" actually have a form of shivers
"Shivers" is a condition that looks similar to stringhalt. It differs in that shivers horses often progress to muscle wasting and weakness, but these severe signs may not show up for years. A horse with classic shivers trembles or quivers and abnormally elevates its tail. As with Monday morning disease, EPSM has been shown to be an underlying condition in many draft horses (and other breeds) with shivers. The abnormal action is apparently caused by a lack of energy to the powerful hind limb muscles. Only further study will determine if shivers has other causes.
Therapy
An important part of the studies began at Cornell, and continued at Oregon State University study has been the evaluation of diet change as a treatment. Horses with EPSM seem not to be able to derive adequate muscle energy from carbohydrates, the main source of energy in grains, sweet feeds, and pelleted horse feeds. The diet change involves decreasing the amount of dietary carbohydrates and replacing them with fat as an energy source. For details see Dietary Recommendations for a Horse with EPSM.
If you have a confirmed EPSM horse in the barn, it may be easiest to feed all your horses the same diet. Feeding a "normal" horse the EPSM-type diet is not harmful. Several nutrition researchers, including Dr. Harold (Skip) Hintz at Cornell University and Dr. David Kronfeld at Virginia-Maryland Veterinary College, have for many years tested the effects of this high-fat diet. They have discovered no ill-effects and have found some indications that this diet is better for all horses.
You might think high-fat feed is much more expensive than feeding other grains, but high-fat feeds are so high in calories that the amount necessary to provide the same number of calories is much less. Fat provides more than twice the calories per volume compared to carbohydrates. For example, 2 cups of oil (approximately one pound) provide about 4,000 calories, whereas one pound of corn, oats, sweet feed, or other commercial feed provides only 1,200 to 1,400 calories. Factor in the potential costs of veterinary care for the affected horses, or even the potential loss of a horse, and the cost of the new diet looks even better.
Good quality hay and pasture are still vitally important; only the grain is changed. The simplest diet consists of replacing a portion of the grain with alfalfa and adding vegetable oil, but these days we have many different ways to achieve an EPSM diet. The best diet for your EPSM horse is one you are happy buying that your horse is happy eating, and that keeps your horse's muscles healthy.
With dietary therapy, many cases of EPSM show 100% improvement. Dietary therapy is most effective when started in the disease's earlier stages. Severely affected draft horses may die, despite having been started on dietary therapy. We believe they die because the disease is so advanced at the time of diagnosis. Unfortunately, the naturally stoic nature of many draft horse can allow sever changes to occur within the muscles without signs of problems for the owner to observe. By the time these horses show obvious problems the disease may be quite advanced and severe. Changing the diet of draft horses from a carbohydrate-based concentrate to a high-fat low-carbohydrate feed may decrease, delay, or even prevent the signs of EPSM in affected horses. For some EPSM horses, diet therapy has been life-saving. Horses on this diet often have improved muscling and increased energy. Most important, they are able to perform with minimal to no muscle damage. Only time will tell just how well diet therapy works.
After dietary fat, exercise is the second most important thing needed by horses with EPSM. Standing in a tie stall or going for long trailer rides only makes these horses worse. Give an EPSM horse as much daily turnout and as much regular work as possible, allowing the horse to maximally utilize the dietary fat. Be careful with warm-ups, though, and don't over-exert the horse when returning it to work after a lay-up 
Beth A. Valentine, DVM, PhD, is involved with EPSM research and other veterinary matters at the College of Veterinary Medicine, Oregon State University. She is this site's virtual vet and co-author of Draft Horses, an Owner's Manual. This article appeared in The Evener 1998 issue of Rural Heritage.
Canker...
From ('The Horse')Canker is an anaerobic (grows in the absence of oxygen) infection in the superficial epithelium of the hoof (the horn-producing tissues of the foot).
Veterinarians believe the invading organism is a part of the bacteroides species, which is similar to what causes "footrot" in sheep. Cases usually are found in
the southeastern United States, but it has been diagnosed all over the country. The bacteria associated with canker causes abnormal keratin production,
or overgrowth of the horn. This excess proliferation occurs underneath the horn, as the infection spreads throughout the epithelium. The horse's owner will
notice the presence of a white or gray matter that is moist and spongy and commonly appears in the sulci region of the hoof. If there is enough infection,
heat might be felt in the hoof, but only in extreme situations. The mystery surrounding canker is its cause. It involves a very strict anaerobic process, and seems to have a multi-factorial pathogenesis. For research we've
tried to recreate canker in the horse, but have never been successful. Our theory at this point is that canker is caused by some sort of trauma. An infection gets inside the hoof capsule and allows the horn to proliferate. It can be tough to get it out once it gets established. Canker is fairly rare, and appears only briefly in veterinary textbooks. Most texts suggest that housing a horse in unsanitary conditions causes the disease,
but I've found that canker is not prejudicial. Farms with the best of stable management and those with the worst can have horses with canker. In our attempts
to recreate the disease, we have packed the frog with manure after injecting what we believe is the invading bacteria, but still have been unable to prove that unsanitary conditions contribute to the onset of canker. Development of canker might have something to do with how the horse is used. Stalled horses with little exercise seem more predisposed to the disease than horses which are active and outdoors. While thrush is a necrotic process, canker is a hypertrophic pododermatitis. Both thrush and canker are found in the same region of the foot, but instead of the tar-like substance evident in horses with thrush, canker resembles rotten cauliflower. Some people say hooves with canker have a distinct odor, but I believe that thrush is much more odiferous than canker. Thrush is an aerobic process caused by another mysterious bacteria, thought to be fusobacterium necrophorus spp., which works superficially and does not undermine tissue. When thrush eats at tissue, the inner tissues of the digit are protected until bacteria gets deep enough to deteriorate more sensitive structures. Canker spreads in live tissue, without the help of oxygen. To eliminate canker, veterinarians have tried many different medications. Suggested treatment is two-fold: 1. Superficial Debridement--First remove horn over the affected area. Make sure that you do this very superficially, because if you draw blood, infection will be driven deeper into the tissue. 2. Be sure to open the infected site to the air, and keep it very clean and dry. We've found that Metronidazole--an antibiotic/microbial-- applied topically or given systemically has worked the best. Systemically, there is no medicine that will cure canker if superficial debridement is not performed. After applying the topical medication, apply a clean, dry bandage that is waterproof. Canker prefers moist conditions, so you must keep the affected area dry. Horses have variable response to treatment. Some cases heal within a week or 10 days, and some cases last for months. Years ago, owners lost some horses to canker. That now is the exception rather than the rule because veterinarians are able to recognize and treat the disease early in its process. Given good, aggressive treatment, a week to 10 days of intensive therapy should have the canker under control. Once your horse is completely rid of canker, the condition is gone. I have never seen it recur. Before healing is complete, however, canker might try to return. So, just when you think you've whipped it, there it goes again.
JEB = Junctional Epydermolysis Bulosa
Genetic disease seen most commonly in American Belgians and Standard Breds (different gene defect in each breed!). Recessive, so living horses can only be carriers and are not affected, but affected foals (born to 2 parents each with the recessive gene) die shortly after birth. Affected foals are born with patches of skin missing, hoof capsules missing or slough off shortly after birth, ulcers in the mouth and sometimes milk teeth already in at birth. All Belgian stallions must be tested for this defect although they can still be registered. A JEB carrier horse shows no outward signs of the disease and the only way you know the horse is a carrier is to have a DNA test ($50) done. The kit can be purchased from UC Davis or the BDHCA. DO NOT BREED CARRIER HORSES!! Am Belgians have about 30% carriers, Brabants have less than 10% carriers.
-KG