February 28, 1988
Reprinted with permission
QUALITY GREEN PASTURES
Horses that are not allowed sufficient grazing
time or who are inefficient grazers may need vitamin
THE EYES HAVE IT
Damage(brown pigment) to a horse's pupil
occurs as a result of vitamin E deficiency
E is for "ease"
Vitamin E may ease the symptoms of motor neuron
disease and other stressors
by Kenneth Marcella, D.V.M.
Equine protozoal myeloencephalitis (EPM) is a parasitic
disease that affects the brain, spinal cord, and nervous
system. It can cause mild signs of incoordination in some
horses and can quickly make other horses so unstable they
cannot get up. It is currently a "popular disease,"
with many horses being tested and treated because of the
recent increase in cases nationwide and the great variability
of clinical signs that makes EPM resemble many other problems.
Equine motor neuron disease (EMND) is another relatively
new disease that affects the nervous system of horses,
specifically those nerves controlling skeletal muscles.
This disease in horses was first described in 1990 and
has since been shown to resemble human amyotropic lateral
sclerosis (Lou Gehrig's disease). Horses with EMND show
a rapid onset of trembling, excessive recumbency, low
head carriage, a constant shifting of weight on the rear
legs, and muscle atrophy.
Equine degenerative myeloencephalopathy (EDM) is a disease
of the spinal cord and brain stem. Affected horses show
ataxia (incoordination), which occurs early in life and
can stabilize or progress to become so severe that the
horse must be euthanized.
What do EPM, EMND, and EDM all have in common? These
three diseases have helped spark a renewed interest in
the role of vitamin E in the horse. Researchers have found
that horses who suffer from EDM have abnormally low levels
of vitamin E, and supplementing the diet with vitamin
E can lessen the disease in those horses already affected
and help prevent it in foals if given before clinical
signs of ataxia occur. Horses with EMND also have been
shown to have low levels of vitamin E in their tissues
The absence of grazing time is a predisposing factor
in EMND, and this reflects the inability of the horse
to utilize pasture as a natural source of vitamin E. EPM
is thought to be at least partially immune-based in that
greater than 50% of all horses have been exposed to the
parasite, while a very small percentage of horses actually
gets the disease. Vitamin E is felt to be an immune system
stimulator and, consequently, vitamin E supplementation
is being highly recommended in affected horses.
These diseases and others have made vitamin E the focus
of research and clinical testing and have changed the
current recommendations for this nutrient in equine diets.
Vitamin E is one of the fat-soluble vitamins along with
A and D. These vitamins must be supplied by the diet.
Quality grass pastures and properly harvested hay are
good natural sources of these vitamins. Horses not allowed
sufficient grazing time or horses that graze poor quality
pasture are more likely to have lower levels of vitamin
E. Supplementation for many horses is, therefore, justified.
There are actually a number of different derivatives of
vitamin E to choose from when trying to supplement equine
diets. One form, d-alpha-tocopherol, is relatively unstable,
and reaction to oxygen in the air causes it to lose potency
quickly. Esterified forms of vitamin E are more stable
and are converted to active forms following absorption
in the body. Another derivative, dl-alpha-tocopherol acetate,
is considered by many nutritionists to be the most potent
form of vitamin E. It is this form that is commonly used
in feed supplements.
There has been a gradual increase in the National Research
Council (NRC) estimates for vitamin E over the past ten
years. Research that has shown improved performance and
some possible benefits to muscle function during exercise
has helped raise the recommended levels.
Effects of E
Stimulation of the immune system is a noted response
to high levels of vitamin E and its effects as a free
radical scavenger have also been documented. Free radicals
are molecules that have an unpaired electron in their
composition. These are unstable molecules and they contribute
to tissue damage at the cellular level. These molecules
are produced in small amounts during normal metabolic
processes but are greatly increased during trauma, stress,
and disease. Vitamin E helps stabilize these radicals
and stops the destructive process. Still other effects
of high vitamin E intake are being noted. William Vandergriff,
Ph.D., an equine nutritionist based in Georgia, feels
that high vitamin E levels are "showing success even
with broodmares in that supplementation during the last
trimester leads to healthier foals and ease in breeding
the mare back." Because of the many beneficial actions
of vitamin E, the NRC recommendations for daily intake
have been raised from 15 IU (International Units) to 80
IU in 1989 to 250 IU in 1997.* Harold Hintz,
Ph.D., a nutritionist at Cornell University, and others
in the veterinary community have further increased those
levels to 450 IU for maintenance, 720 IU for late gestation,
950 IU for lactation, and 1,000 IU for intense work. There
are reports from England and Ireland of trainers using
up to 15,000 IU daily in attempts to get improved performance.
While there have been no reports of vitamin E toxicity
in the horse, long-term effects of such high levels have
not been adequately researched and most nutritionists
are reluctant to recommend them.
Which horses should br given supplemental vitamin
Any horse at risk
for showing signs of EPM, EMND, or EDM
6,000 to 10,000 IU
Young foals or aged
horses. Horses on poor pasture or kept in stalls.
Diseased, injured or stressed horses
400 to 600 IU
Broodmares in late
in intense training or competition
Many supplements have been released on the market recently,
however, which do supply higher levels of vitamin E. These
products make it easy to add vitamin E at levels up to
5,000 IU daily. Caution is urged to keep the selenium
level at 1.5 to 2 milligrams daily even when feeding high
amounts of vitamin E. Selenium is another important dietary
compound that works synergistically with vitamin E and
is sometimes sold in supplement form together with vitamin
E. Problems can occur if such a vitamin E/selenium supplement
is fed to achieve beneficial effects from high levels
of vitamin E. The dose of selenium is then increased and
toxicity problems can definitely occur from this mineral.
What to give
So which horses should be given supplemental vitamin
E? Any horse at risk for or showing signs of the nervous
system or neuromuscular diseases mentioned earlier. Horses
with EPM, EMND, and EDM should receive between 6,000 IU
to 10,000 IU daily. Young foals and older horses should
receive supplementation in the range of 400 IU to 600
IU daily. Horses on poor pasture, in climates where pasture
grass is not plentiful, and horses kept predominantly
in stalls (showhorses or racehorses) should receive similar
supplementation Diseased, injured, and stressed horses
may also benefit from vitamin E. Broodmares during their
last trimester through lactation and rebreeding should
also receive higher levels of this vitamin. While it will
not protect against all diseases and health problems,
there is considerable evidence that vitamin E at high
doses can lead to healthier horses. Further research may
even make the function and benefits of this unique vitamin
clearer. But as long as it helps prevent and treat new
debilitating diseases currently affecting the central
nervous systems and spinal cords of our horses, vitamin
E supplementation makes sense.
Kenneth Marcella, D.V.M.. is an equine veterinarian whose
practice is based in Canton, Georgia.
*Ed.: After having contacted the NRC,
we could not verify a 1997 change to the RDA for vitamin