EPSM
(Muscle Disease in Draft Horses)
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--------------- A NEWLY RECOGNIZED
MUSCLE DISEASE IN DRAFT HORSES ---------- Researchers are involved in an ongoing study of a muscle disease that could affect all draft horse owners, including those with carriage horses, working farm horses, pulling horses, show horses, and breeding horses. The muscle disease of interest is a newly-recognized disease, although it has likely been around for hundreds of years. This disease, known as Equine Polysaccharide Storage Myopathy (or EPSM for short), has been identified in many horse breeds, but appears to be a particularly common, severe, and difficult to detect disease in the draft breeds. To date, EPSM has been confirmed or suspected in over 150 draft horses, including Belgians, Percherons, Clydesdales, Shires, Haflinger, Norwegian Fjord, Suffolk, Irish Draft, draft crosses, and a draft mule. One of these horses had been imported from England. 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 draft horses, as a cause of poor performance, "shivers" and other abnormal hind limb gaits and, the most devastating of all, as causing recumbency due to weakness ("down horses") either during work, associated with foaling, at rest, or following general anesthesia. Affected horses can easily be misdiagnosed as foaling complications, colic, or other diseases. Another suspected sign is increased temperature (hyperthermia) during recovery from anesthesia. The role this disease may play in post-anesthetic complications is particularly important, as draft horses have been known for many years to be prone to problems associated with general anesthesia. The results of continued studies may provide treatments for horses that would otherwise die or be euthanized because of inability to rise.
An important part of the on-going studies has been the
evaluation of the effect of diet change as a treatment. Horses with EPSM
seem not to be able to derive adequate muscle energy from soluble
carbohydrates (starches and sugars), which are the main source of energy
in grains, sweet feeds, and many pelleted horse feeds. A different type
of carbohydrate, insoluble carbohydrate, (along with protein) is also a
major source of energy in hay and pasture, but the diet change does not
affect the feeding of hay or allowing pasture grazing. The diet change
involves decreasing the amount of dietary starch and sugar, and
replacing them with fat as an energy source. There are many ways to add
fat to a horse's diet, including vegetable oil, powdered animal fat, and
commercial feeds designed to be high in fat. To date, this dietary
therapy appears to be extremely effective, with many cases showing 100%
improvement. It does appear, however, that dietary therapy is most
effective when it is started in earlier stages of the disease. At least
10 severely affected draft horses that were started on dietary therapy
still progressed to death, and it is suspected that this is because the
disease was so advanced at the time of diagnosis. It may be that
changing the diet of draft horses from a soluble carbohydrate-based
concentrate to a high fat, low starch and sugar feed may decrease,
delay, or even prevent the signs of EPSM in affected horses. Even horses
not on grain are at risk of developing signs of the disease, as they are
still not able to derive enough energy from forage.
Affected draft horses may appear completely normal for
many years. EPSM may result in slightly abnormal blood levels of muscle
enzymes, but EPSM horses may also have normal muscle enzyme levels. At
this time, diagnosis is best made by examining a muscle biopsy for the
characteristic changes. The biopsy is taken while the horse is standing
and sedated, and the site of the biopsy (the muscle of the caudal rump)
is injected with local anesthetic. This is a simple procedure with
minimal resulting scarring. Testing for EPSM can provide extremely
valuable, perhaps life-saving, information to the draft horse owner.
Many horses with suspected EPSM have been put on a high
fat, low carbohydrate diet without biopsy confirmation, as a response to
diet indicates that our diagnosis was correct. Some folks, however, feel
better knowing for certain whether or not their horse has EPSM before
they will change diet, and have requested that their veterinarian
perform a biopsy to be sent to Oregon State University.
Answers to some common questions about EPSM in draft horses: WHAT EXACTLY ARE THE SIGNS OF EQUINE POLYSACCHARIDE STORAGE MYOPATHY IN DRAFT HORSES? - Lack or loss of muscle mass or conditioning, especially in the shoulder or hind quarters - "Stringhalt", "shivers", or fibrotic myopathy-type gait, especially when backing or turning (may look like a "locking stifle") - Trembling, especially after exercise - "Tying up" - Difficulty rising, backing, or reluctance to back - Lack of energy, stumbling - Poor performance - Reluctance to pick up feet for shoeing, etc. - Lifting or "stomping" of hind limb or limbs, especially while standing - Episodes of "colic", especially after exercise - Slightly stiff, awkward, or short strided hind limb gait (often have no "hock action") - Recumbency with inability to rise WHAT IS THE DIFFERENCE BETWEEN EPSM AND "MONDAY MORNING DISEASE"?
"Monday Morning Disease" is the disease 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 what is often called "tying up" in
saddle horses, in which muscles become stiff, begin to degenerate, and
the horse will stop moving and may even 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 urine
color, the disease has also been called "azoturia". Other
names include "set fast" and "exertional myopathy"
or "exertional rhabdomyolysis".
It is thought that the the massive muscle damage that
occurs in EPSM drafts occurs due to the lack of muscle energy. The
common finding of slightly increased levels of muscle enzymes in the
blood in apparently normal, or only mildly affected EPSM horses suggests
that these horses often have low-level muscle injury during exercise.
What it is that puts them "over the edge" into massive muscle
injury is still not clear. But studies of muscle from horses that have
had signs of "Monday Morning Disease" show that EPSM is a
common underlying condition and, in these horses, EPSM is thought to be
the cause of the disease.
Whether or not all horses with "Monday Morning
Disease" also have EPSM remains to be proven, although to date
every horse that has "tied up", even when it occurred years
before biopsy, has been biopsy positive for EPSM and has improved
dramatically following diet change. (Note: This also applies to
non-draft related horses that have problems with "tying up").
WHAT ABOUT EPSM AND "SHIVERS"?
"Shivers" is a condition in which abnormal hind
leg action is seen, especially when the horse backs or turns. It is very
similar to "stringhalt" (sometimes called "springhalt").
Classic "shivers" horses also have a tail elevation and
quivering, but the two disorders are very similar in early stages.
Horses with "stringhalt" will show no other signs, but
"shivers" is associated with progressive muscle wasting and
weakness, although it may be years before these severe signs are seen
(see accompanying article on "shivers").
Similar to "Monday Morning Disease", EPSM has
been shown to be an underlying condition in several draft horses with
"shivers," and lack of energy to the powerful hind limb
muscles apparently results in the abnormal action, which may be due to
muscle cramping. Only further study will determine if there are other
causes of "shivers".
HOW WELL DOES DIET THERAPY REALLY WORK?
Only time will tell, but for some EPSM horses diet
therapy has been life-saving. Horses on this diet often have improved
muscling, increased energy, and, most-importantly, are able to perform
with minimal to no muscle damage.
IS THERE ANYTHING ELSE THAT IS IMPORTANT TO KNOW ABOUT TREATING EPSM?
Yes, and that is that exercise is the second most
important thing that horses with EPSM need after dietary fat. Standing
in a tie stall only makes these horses worse. Giving a horse with EPSM
as much daily turnout and as much regular work as possible is critical,
and allows the horse to maximally utilize the dietary fat.
WHAT EXACTLY IS THIS DIET?
This diet aims to provide at least 20-25% of total daily
calories from fat. As stated above, there are many ways to decrease the
carbohydrates and increase the fat in the horses diet. Good quality hay
and pasture are still vitally important, it is only the grain that is
being changed. The simplest diet consists of replacing grain with
alfalfa pellets with added vegetable oil. For a 1000 lb horse, this diet
consists of approximately 5 lbs of alfalfa pellets with 2 cups of oil
per day. A selenium supplement to provide 1 mg selenium per day to a
1000 lb horse is essential in most parts of North America, as the hay
and grass contain very little of this essential mineral. As many
selenium supplements also contain vitamin E, and vitamin E is an
essential vitamin that can be fed at high levels with no signs of
toxicity, most EPSM horses are supplemented with both vitamin E and
selenium. For draft horses, the amount of pellets is increased according
to the horse's needs, and from 3-4 cups of vegetable oil are fed. The
oil can be soy, canola, or corn oil, although corn oil is the most
expensive. Buying vegetable oil in bulk from a restaurant supply can
save a lot of money. Another source of fat is powdered animal fat, which
can be purchased in large quantities at a relatively low price. Be
aware, however, that most of the animal fat products are designed to be
fed to ruminants, and horses will not be able to digest them fully.
There are, however, some powdered animal fat products designed to be fed
to horses and pigs, and these are thought to be more digestible.
Powdered rice bran is another source of fat but, as these feeds are only
15-20% fat instead of 100% fat, 5-6 times more will need to be added to
the feed to supply the needed calories from fat. Recent studies have
shown that rice bran also contains starch and sugar (about 22% in one
product), and so it is not possible to achieve the right calorie balance
with rice bran alone. Rice bran can help to add some fat and also to
soak up added oil, though. There is no problem with mixing rice bran and
oil, no matter what anyone might try to tell you.
Some horses will not eat alfalfa pellets, at least not in
high volumes, and for these horses we have looked to feeding some of the
commercial diets that are higher in fat. Purina® Strategy®, Purina®
Athlete®, Nutrena™ Compete®, and some of the Blue Seal® feeds have
been used successfully for many EPSM horses. Added fat is still
essential, as these feeds, combined with the horse's hay or pasture, do
not provide the minimum of 20-25% of total daily calories from fat that
we are aiming for. The manufacturers of horse feeds have recognized the
value of feeding increased levels of fat to horses, and many new
products are coming on the market that have an increased fat level. To
date, however, none contain the level of fat and the concurrent
reduction of starch and sugar necessary to successfully treat a horse
with EPSM. Remember, we are trying to feed such that at least 20-25% of
the total daily calories come from fat, not just looking for a 20% fat
feed. This equates to about 1 pint (1 lb) of fat/day per 1000 lbs of
horse. Maintaining a moderately high level of protein may also be
important, especially in horses with muscle wasting.
CAN A "NORMAL" HORSE BE FED THIS TYPE OF DIET?
Without biopsy confirmation of EPSM, the disease may only
be suspected based on clinical signs or slight increases in blood levels
of muscle enzymes. In some situations, with a confirmed EPSM horse in
the barn, it may be easiest to feed all horses the same diet. There is
no danger in feeding a "normal" horse this type of diet.
Several nutrition researchers, including Dr. Harold (Skip) Hintz at
Cornell University and Dr. David Kronfeld at Virginia-Maryland
Veterinary College, have been testing the effect of a high fat diet in
horses for many years. They have shown no ill-effects and, in some
instances, have suggested that this type of diet is better for all
horses. For example, with high fat feeds horses produce less body heat
during work. They are less prone to colic or founder. There is an
improved power to weight ratio due to the ability to reduce the weight
of feed in the intestine ("gut ballast"). This latter effect
may be of particular interest to owners of pulling horses. Dr. Kronfeld
has also speculated that the reduced carbon dioxide production during
exercise of horses on a high fat diet may benefit horses with lung
disorders such as "heaves", which cause reduction in lung
capacity.
HOW MUCH IS THIS TYPE OF FEEDING GOING TO COST?
Although it would initially appear that this type of feed
is much more expensive than feeding other grains, this is not really the
case. High fat feeds are so high in calories that the amount of feed
necessary to provide the same amount of calories is much less. Fat
provides more than twice the calories per volume that carbohydrates do.
For example, 2 cups of oil (approximately 1 lb) provide about 4000
Calories, whereas 1 lb of corn, oats, sweet feed or other commercial
feeds will provide only about 1200-1400 Calories. With a high fat diet
you may be able to reduce the amount of hay fed and still maintain good
body condition (of course, hay and other forage is critical to the
horse's digestive system, but you may be able to feed a less rich hay or
less volume - I know some folks that feed their drafts a bale of hay per
feeding!). If you factor in the potential costs of veterinary care for
affected horses, or even the potential loss of an affected horse, the
additional cost of this type of feed is much less. As is always true, it
will cost a bit more to feed your horse the absolutely best diet
possible. However, this type of diet is likely to extend the productive
life of the horse, whether it be used for working, pleasure, or
breeding.
HOW COMMON IS THIS DISEASE IN DRAFT HORSES?
Although more studies are necessary to confirm this, our
preliminary findings indicate that EPSM is far more common in draft
horses than we initially thought.Screening studies of all draft horses
at a farm, and from all draft horses autopsied for whatever reason,
indicates an incidence of well over 50%. This means that if you have 2
draft horses or draft crosses, the likelihood that at least 1 horse is
affected is very high. We have studied farms in which 8 of 10 horses
were affected. Although many were not showing any obvious signs of the
disease at that time, and some owners have chosen not to change anything
in their affected horse's diet, at least they know what to look for, and
what to do if their EPSM horses begin to show signs of the disease. Of
course, if the first sign of a problem is a horse that is down and
unable to rise, the chances of
pulling that horse through, even with stomach tubing with vegetable oil and/or intravenous treatment with lipid, are only 50% or less. This may very well prove to be a disease that is more easily prevented than treated.
IF YOU HAVE OTHER QUESTIONS ABOUT EPSM IN DRAFT OR DRAFT
CROSS HORSES (OR OTHER BREEDS), CONTACT:
Dr. Beth A. Valentine
Department of Biomedical Sciences College of Veterinary Medicine Oregon State University Magruder 142 Corvallis, OR 97331 Phone: 541-737-5061 Fax: 541-737-6817 e-mail: beth.valentine@orst.edu
(c) 2001 Vita-Flex Nutrition, Inc.
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