Diabetes in Horses
Ken Marcella, DVM

Diabetes is one of the most common problems for humans, and it
was long thought that the problem did not exist in the equine
world. A review of veterinary literature over the last 50 years
shows only a small number of cases of equine diabetes. These
recorded cases were mostly caused by pancreatic disease or by
tumors in the pituitary gland and were few and far between. That
may be changing as veterinary researchers identify more and more
horses that seem to be suffering from various stages of insulin
resistance, the early stages of what will eventually lead to
Adult-Onset or Type II Diabetes.

No one is sure why the veterinary community is seeing more and
more cases of insulin resistance. Perhaps, because horses are
living longer with increasingly better medical care, we are
finding an increase in diseases that develop in later years.
These cases may have always been present but were undiagnosed,
and recent improvements in diagnostics and the increased
attention older horses now receive might be helping us recognize
these cases.

Adult-Onset Diabetes develops slowly as the person or animal
becomes an adult. The earlier condition leading to Type II
Diabetes is called insulin resistance. In this slowly developing
condition, the body's cells become less and less sensitive to the
natural insulin that is being produced. Insulin is a hormone that
is secreted or produced and released from the pancreas. Insulin
is released in response to an increase in glucose levels in the
blood following a meal containing sugars or starches. Insulin
then stimulates cells in the body to take up this circulating
glucose from the blood. Once in the cells, glucose is used for
energy or it is converted for storage as glycogen or fat. Horses
suffering from insulin resistance show an eventual breakdown of
this system.

As the body's cells become less and less sensitive to insulin,
the body responds simply by producing more and more insulin.
These higher levels serve to regulate blood glucose for a while.
Diagnostic testing is now being done to identify these horses
suspected of being in the early stage of insulin resistance.
Often, before many clinical signs are even noticed, these tests
show horses to have normal glucose levels but with various stages
of elevated insulin levels. This stage of disease is being called
Impaired Glucose Tolerance (IGT) and is the condition seen in
most horses. Eventually the body's cells fail to respond to these
increasing levels of insulin and this leads to exhaustion and
failure of the insulin-producing cells. At this point the horse
can be technically called a diabetic, though the exact stages and
the naming of those stages is more of an academic exercise. What
is important to the horse and its owner is that at some point the
body fails in its need to regulate and maintain glucose
metabolism, use and storage.

Horses suffering from impaired glucose tolerance show a variety
of clinical signs. Typically these are overweight horses that
maintain their weight despite reduced feeding on the part of
their owners. In fact, these horses often have excess fat
deposits in their crests, backs and rumps. These fat deposits
result from the body's inability to use glucose, so it is
inappropriately stored as fat. It is interesting to note that
some researchers feel that this fat storage ability may have
helped these diabetes-prone horses to be evolutionarily selected.
An ability to remain fat on meager rations and to store fat would
have been advantageous to horses in times of drought or famine.
These fat-preserving horses would have survived better and had
better chances of reproducing, so according to theory, the
genetics of these horses may have been selected for over those of
other non-insulin resistant horses.

Affected horses have reduced energy levels. They need exercise to
control their weight and metabolism but owners report that it is
often difficult to get these horses to work. Skin conditions are
common in these horses and simple cases of rain rot or pasture
scald seem to be more serious and to take longer to resolve.
Complications due to recurrent laminitis or founder, however,
seem to be the single biggest problem in insulin-resistant
horses. Foot disease is the single most common complication
leading to hospitalization in Type II diabetic humans. The
disease causes complications with peripheral blood flow and
inflammation in the tissues of the toes. Dr. C.C. Pollitt of the
Veterinary School at the University of Queensland in Australia
has been doing research on laminitis that strongly suggests that
this disease of horses is linked to altered glucose metabolism in
the cells of the sensitive laminae in the hoof. Damage to these
particular areas leads to disruption of the structure of the foot
and to the characteristic "rotation" that characterizes this
disease.

Diet and Exercise
As more research is completed, perhaps some of the more advanced
drugs currently being used to help human diabetics can be used to
help horses. Much more research needs to be done and it is
important that horses with insulin resistance be accurately
diagnosed. Many of these horses show clinical signs that are
similar to horses with Cushing's disease. (See "The Twilight
Zone," The Mane Points, Spring 2002.) Research into normal and
disease-related insulin levels should soon allow veterinarians to
better distinguish between these two diseases. It is important
that owners do everything they can for these horses, until the
point when research provides some pharmacological help.


The first treatment for diabetics always involves diet and
exercise, and horses are no different. These horses should be fed
low grain diets to reduce the amount of starch and sugar. Good
quality hay is the basis of an insulin-resistant horse's feeding
plan. Additional energy, if needed, can be added in the form of
beet pulp or rice bran. Vitamin and mineral supplementation is
crucial with attention to levels of chromium, zinc and magnesium,
as these elements have been shown to affect insulin function and
glucose metabolism. Triple Crown 12% Supplement and 30%
Supplement and Triple Crown Lite have much lower feeding rates
than regular grain-based horse feeds. For most grass and mixed
hays, Triple Crown 12% or Triple Crown Lite would be appropriate.

If your hay has a crude protein content of less than 8%, feed
Triple Crown 30% Supplement instead. For a 1,000 pound horse,
feeding 15 pounds of hay and two pounds of Triple Crown Lite
would meet maintenance requirements. Feeding an additional 1 to
1.5 pounds of Triple Crown Rice Bran daily for a 1,000 pound
horse would provide the additional calories needed for light
activity.

An exercise program should be initiated based on the particular
horse's condition and ability. Routine easy exercise on a regular
basis is much preferred to sporadic intense exercise. These
simple steps can improve glucose regulation and slow the
development of insulin resistance.

Kenneth Marcella, D.V.M., is based at the Chattahoochee Equine
Center in Canton, Ga.