EPSMMuscle Disease in Draft
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
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 horsesmuscles
become stiff and begin to degenerate; the horse stops moving and may go down.
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.
(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.
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
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
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
Horses, an Owner's Manual.
This article appeared in
The Evener 1998