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.
Source: Pet Care Tips