The Effects of Chronic Insulin Resistance in Horses

Equine metabolic syndrome--EMS, also called chronic insulin resistance--occurs in horses five to 10 years of age, advises Dr. Nicholas Frank of the University of Tennessee. As these horses age, they typically develop another hormonal disorder called Cushing's sydrome and or/diabetes. Early diagnosis, dietary changes and weight loss can prevent the development of diabetes and effectively manage both EMS and Cushing's, Frank says.

  1. Blood Levels

    • The horse's pancreas produces hormone insulin to control glucose levels in the body. The insulin signals muscle, fat and liver cells to pull glucose from the horse's blood, and store it in body tissue as glycogen--the chief energy-producing carbohydrate in the bodies of animals. With the onset of EMS, insulin levels in the blood spike, resulting in normal blood sugar levels. As the disease progresses, blood-sugar levels increase, as do insulin levels, effectively causing a disease very similar to Type 2 diabetes in humans, reports Dr. Stacey Oke of TheHorse.com.

    Other Disease Issues

    • Increased levels of sugar in the blood cause a loss of cellular energy and force the horse's body cells to malfunction, leading to organ disease and other systemic problems. Insulin-resistant horses often show elevated amount of lipids--fatty cells--in the blood and increased blood pressure. Affected horses commonly have cardiovascular disease and kidney failure. According to Dr. Thomas Schell of Timbercreek Veterinary Hospital in Jonesboro, N.C., these animals show a predisposition to laminitis--a painful and sometimes fatal disease of the hoof. He states that while "the exact link between insulin resistance and laminitis in the horse has yet to be discovered," veterinary scientists find a distinct correlation between the breakdown of the lamina cells--the hoof lining--and the animal's increased blood glucose. When the hoof lamina deteriorates, the coffin bone--the main bone inside the hoof--turns, pushing through the bottom of the hoof and causing painful, and sometimes fatal, lameness.

    Fat Deposits

    • The breeds predisposed to insulin resistance include all pony breeds: Morgans, Norwegian Fjords and Paso Finos--all horses with a propensity to gain weight and become obese. According to Dr. Dana Zimmel of the University of Florida, most animals that develop EMS show signs of obesity several years prior to diagnosis with the disease. Mares may show abnormal reproductive cycles linked to the obesity. Affected horses appear with fat deposits around the sheath, the tailhead and in the depressed area above the eye. They also occasionally show fatty masses under the skin of the trunk.