By Neely Walker, PhD.

Feeding your horse is one of the most important factors in maintaining its overall health and performance.   When horses digest feed, carbohydrates produce glucose (sugar), which becomes the horse’s main source of energy.  Once the body recognizes the increase in available glucose, insulin is produced to regulate the glucose concentration and use throughout the body.  Insulin resistance (IR) occurs when the body is no longer sensitive to the actions of insulin.  Therefore, a horse that is insulin resistant will require higher quantities of insulin to properly utilize the available glucose from digested feed.

The cause of Insulin Resistance in horses is not fully understood and it is likely that multiple factors contribute to this condition including diet, obesity, age, activity level, and genetics. Modern feeding programs usually include high sugar/starch which causes an increase in glucose and the amount of insulin required to regulate it.  Research has shown that horses that are fed a high sugar/starch diet, compared to horses that are fed a high fiber/fat diet, were more likely to develop insulin resistance.  Obese horses are more likely to become insulin resistant; however, even lean horses that can be classified as “easy keepers” can also develop this disorder.  Horses over the age of 20 are prone to developing endocrine dysfunction and as a result also develop IR.  The level of activity your horse has also plays a role in Insulin resistance development.  Regular exercise will utilize the excess glucose, thus causing a reduction of insulin; therefore, active horses have a reduced chance of developing IR.

Horses that are Insulin Resistant often have a body condition score of 6 or higher with irregular fat deposits, can be described as “easy keepers,” and may have bouts of unexplained sore hooves and laminitis.  If you suspect your horse may be insulin resistant, it is important that you have your veterinarian diagnose it as soon as possible.  If untreated, insulin resistance can lead to decreased pancreatic function and can potentially cause the development of type II diabetes.

It is important to note that management practices utilized in the first 10 years of a horses’ life can predispose it to becoming insulin resistant.  Prevention is always preferred.  The following management techniques can help you treat and prevent insulin resistance.

• Avoid obesity (body condition score of 7 or higher) by adjusting your feeding protocol.
• Limit grazing, especially in the spring and fall when cool grasses contain the most sugar.
• Limit concentrates and feed grain high in sugar and starch (i.e. NO MOLASSAS); use only if needed.
• Provide exercise and turn out time for your horse. Turn out should be done in a dry lot or an arena to reduce the chance of consuming high starch grasses.
• Maintain adequate hoof care to help reduce future laminitis.
• Ensure a proper diet that is specific to your horse. Many IR horses that are fed a restricted diet do not get all of the required nutrients.  Work with your veterinarian or a nutritional consultant to determine if additional supplements are needed.

Insulin resistance in horses can create a management challenge for owners and decrease overall performance.  If you suspect your horse may be suffering with IR contact your veterinarian immediately.  Maintaining a healthy balance between diet and exercise can help prevent insulin resistance in your horse.

References:

1. Frank, N. 2006. Insulin Resistance in Horses. Endocrinology. Vol 52, pg 51-53.
2. Adams, M. 2009. Feeding the Insulin Resistant Horse. MFA Inc. FactSheet.
3. Treiber, K., Kronfeld, D., & R. Geor. 2006. Insulin Resistance in Equids: Possible Role in Laminitis. Journal of Nutrition. Vol. 136 no. 7 pg 2094s-2098s.  [painting:  Hombre a Cavallo, by Botero]