There’s been a lot of hype lately surrounding metabolic disorders. Just as obesity and diabetes are becoming more prevalent in humans, we are seeing similar diseases cropping up in horses at an equally alarming rate. In order to get ahead of the curve, we must understand what equine insulin resistance is, how it can be prevented, and what we can do about it. To get some answers, Equine Wellness turned to veterinarian and researcher Dr. Frank Gravlee.

EW: What is equine insulin resistance?

Dr. Frank: There is considerable diversity in terminology, causes, diagnostics, treatment and management in the broad subject of equine metabolic diseases. “Insulin resistance” (IR) is the accepted term for increased blood glucose, in combination with normal to increased levels of blood insulin. In a normally functioning system, glucose in the bloodstream is transported into the cells by the action of insulin.

In the case of equine insulin resistance, this glucose transport function is impaired, resulting in an increase of glucose in the circulatory system, and a decrease of glucose within the cells. This excess of glucose in the circulatory system signals the pancreas to secrete more insulin in an attempt to bring the blood glucose back to normal. The end result is an increase in both insulin and glucose in the circulatory system, and a decrease in glucose in the tissue – thus the term “insulin resistance”.

EW: What causes it?

Dr. Frank: A question that remains to be answered is whether insulin resistance (IR) is a symptom resulting from other metabolic dysfunctions, or a primary disease. For example, a fever in an animal is a symptom that can be caused by many different diseases. Research has shown that fat cells secrete hormones that directly affect insulin activity, with obesity multiplying this effect. On the other hand, IR could be a primary disease, such as that occurring due to an acquired or genetic defect in energy metabolism. An example of a genetic primary disorder is glycogen storage disease.

The relationships between metabolic mechanisms leading to or resulting from IR are complex. A major point to understand is the “disconnect” between calories consumed and calories utilized. When horses consume more calories than they need, they store the calories as fatty tissue. When they are burning more calories than they are fed, they utilize these fat reserves for energy. When this delicate balance is upset, the horse is at risk for metabolic problems, including insulin resistance. For example, since many modern horses are often overfed and do very little work, their situation could be compared to a person with a desk job who eats like a professional athlete at a training table. The result will be fat storage and an increased risk of metabolic diseases, which include insulin resistance as a symptom.

EW: How is a horse diagnosed with equine insulin resistance? What can happen if he remains undiagnosed?

Dr. Frank: Some of the early warning signs for equine insulin resistance include:

• Abnormal weight gain or weight loss
• Increased or excessive water consumption
• Loss of stamina and muscle tone
• Tendency to develop laminitis or colic
• Abdominal bloating
• Increased blood triglyceride levels

A definitive diagnosis is accomplished by your veterinarian, utilizing blood tests. These tests could include a series of blood samples drawn before and after either administration of an injection of glucose, or a feeding of grain. Sophisticated glucose challenge tests can be performed in an equine clinic or hospital setting.

Insulin resistance is likely an “early warning” of additional metabolic related diseases, including colic and laminitis, and endocrine related problems such as Cushing’s. If the horse is diagnosed at an early stage, it can allow the attending veterinarian to take preventive rather than “treatment” measures.

EW: What is the prognosis for a horse with insulin resistance, in terms of performance and quality of life?

Dr. Frank: The prognosis is influenced by the type of care. The caretaker must understand the nature of the disease, and be willing to carry out the veterinarian’s instructions. With the right care, many horses can return to previous activities, provided proper attention has been given to any disorders related to creating IR, or disorders that are the result of IR.

EW: What feeding and care practices should you observe once you know you have an insulin resistant horse?

Dr. Frank: Feeding and care should be under the direct supervision of a veterinarian.

• The vet will first attempt to establish the cause of the excess blood glucose and insulin, and treat or manage the cause. Examples of contributing factors include excess calorie consumption, lack of exercise, Cushing’s, medications such as glucocorticoids, and hypothyroidism.

• Each horse should be fed and cared for as an individual. A strict weight control program should be implemented with regards to total energy intake, and with a careful consideration of balance between sugars, carbohydrates and fats. Strict attention should be paid to the restriction of soluble carbohydrate intake. There should be periodic insulin, glucose, thyroid and adrenal monitoring, utilizing the appropriate blood tests.

• The veterinarian will likely prescribe an exercise program appropriate for the horse. The program will depend on the individual horse and his response to treatment.

• Any associated conditions should be addressed, such as laminitis, colic and structural hoof damage resulting from excess weight. Too much weight can also result in other lameness conditions.

EW: What feeding and care practices should you avoid with equine insulin resistance?

Dr. Frank: The first step is to limit the consumption of soluble carbohydrates (sugars and starches) found in high levels in some bagged feeds and forage.

If there’s a need for additional action, limit cellulose by restricting bran or sugar beet pulp, and increase lignin intake with “high stem” content hay or straw. Assure adequate nutrient intake by supplying a product designed to balance hay and pasture without contributing to calorie intake.

EW: Are there any ways to prevent insulin resistance?

Dr. Frank: The first step to minimizing problems associated with IR should be to furnish all the nutrients your horse needs, utilizing grass hay or pasture in combination with a pasture/hay nutrient fortifier. Using this approach, the required calorie intake can be controlled and separated from other nutrients. The second step, if necessary to control weight, is to reduce the grade of hay or pasture, or substitute straw for some of the hay.

EW: Is equine insulin resistance on the rise, and if so, why?

Dr. Frank: Equine insulin resistance and other metabolic syndromes are being diagnosed with increasing frequency. When calorie intake is directly tied to other nutrients, the only method of reducing calories is to reduce the other nutrients, thereby increasing the risk of deficiencies and inefficient nutrient utilization. The resulting “calorie imbalance” either contributes to or creates metabolic problems, including IR.

With “high energy content varieties”, irrigation and fertilizers, today’s hays and pastures are often more carbohydrate and sugar dense. This increased calorie content is good for cattle and commercial milk production, but may be inappropriate for the IR horse. It may be necessary to limit grazing or dilute the hay with straw or “high stem content” hay.

Another contributing factor to the increased incidence of equine insulin resistance may be the number of horses receiving less exercise.

As we learn more about insulin resistance, there will be additional articles and books written on the subject. From a practical viewpoint, all this will boil down to one fact: there are many ways to feed more calories than are being burned. The calorie imbalance that results will invariably lead to many problems.

Dr. Frank Gravlee graduated from Auburn University School of Medicine and practice d veterinary medicine for several years before attending graduate school at MIT . During a three-year residency in nutritional pathology he received a masters degree in nutritional biochemistry and intermediary metabolism. In 1973, he founded Life Data Labs to determine equine nutritional deficiencies through laboratory testing, and developed individualized feeding programs to correct the deficiencies he discovered. After ten years of research, he launched Farrier’s Formula.