Causes, Symptoms, Prevention and Treatment 

What is insulin resistance?

‘Insulin resistance’ 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 insulin resistance, this glucose transport function is impaired, resulting in an increase of glucose inside the circulatory system and a decrease of glucose within the cells. This excess of glucose in the circulatory system signals the pancreas to secrete even 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.

What causes insulin resistance?

The relationships between metabolic mechanisms leading to or resulting from IR are complex. It is unclear whether insulin resistance is a symptom resulting from other metabolic dysfunctions or a primary disease.

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 the balance between calories consumed and calories used is upset, the horse is at risk for metabolic problems, including insulin resistance.

For example, an overfed horse that does very little work (or none), will increase his fat storages. This will result in an increased risk of metabolic diseases which include insulin resistance as a contributing factor.

Early signs of Insulin Resistant Horse:

• 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 can be accomplished by your veterinarian utilizing blood tests. The 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 Cushings. If the horse is diagnosed at an early stage, it can allow the attending veterinarian to take preventative measures rather than treatment measures in the care of the horse.

What is the prognosis for a horse with IR?

The prognosis, in terms of performance and quality of life, depends on the type and quality of the care. Many times, a horse can return to previous activities provided the proper attention has been given to any disorders related to or resulting from IR.

The caretaker must understand the nature of the disease and be willing to carry out the instructions given by the attending veterinarian.

What feeding and care practices should be implemented for IR horses?

The feeding and care should be under the direct supervision of a veterinarian. Issues the veterinarian may address are as follows:

• The veterinarian 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, Cushings, administration of medications such as glucocorticoids, and hypothyroidism.
• 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 a specialized exercise program for the horse.
• Any associated conditions should be addressed such as laminitis, colic and structural hoof damage resulting from excess weight. The excess weight can also result in other lameness related conditions.

What should be avoided when caring for an IR horse?

The use of feed high in starches and carbohydrates should be avoided. The horse owner should limit the consumption of soluble carbohydrates (sugars and starches) present in high levels in some bagged feeds and forage.

If there is need to take 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.

Are there any ways to prevent IR?

The first step to minimize problems associated with IR should be to avoid compounded feeds. Instead, furnish a balanced diet utilizing grass hay or pasture and a hay/pasture balancer.

An excellent balancer is Barn Bag^®, a concentrated nutrient source low in calories and starches.

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. 

Why is IR on the rise?

There are several contributing factors:

• In compounded feeds, calorie intake is directly tied to other nutrients. Therefore, when we reduce or increase calorie intake we are also under or over supplementing other nutrients. The resulting imbalance may contribute to metabolic problems, including IR.
• Today’s hays and pastures are often more carbohydrate and sugar dense with the “high energy content varieties”, irrigation and fertilizers. The increased calorie content is good for cattle and commercial milk production, but is inappropriate for many horses. It may be necessary to limit grazing, dilute the hay with straw or feed “high stem content” hay.
• Another contributing factor in the increased incidence of IR may be the number of horses that are receiving less exercise.
• Further contributing to lack of exercise is that modern horses do not have to search for forage or water, as these are usually under their nose.

From a practical matter, all this ‘boils down’ to the fact: if there’s either an imbalance between calories consumed and calories utilized or imbalanced nutrient intake, problems will develop over time.

J. Frank Gravlee, DVM, MS, CNS 
Founder of Life Data Labs, Inc. 
Developer of Farrier’s Formula® 
H. Scott Gravlee, DVM, CNS 
Equine Nutrition Consultant

Learn More About Barn Bag^®