Grasping Insulin Resistance in Horses

To manage horses with insulin issues successfully, a critical first step is understanding what insulin is, what goes wrong, and why it matters.

Photo: iStock

Two leading researchers explain insulin's effects on the body and how to manage the IR horse

Raise your hand if you’ve ever wondered, “Wait a minute, which is the bad one—insulin sensitivity or insulin resistance? After all, if too much insulin is bad, wouldn’t we want our horses to be resistant to it?” The whole talk of insulin sensitivity and resistance can seem pretty confusing. And it only adds to the stress of dealing with a horse who has or might have insulin-related issues. 

To manage horses with insulin issues successfully, a critical first step is simply understanding what insulin is, what goes wrong, and why it matters. The second? Care for them according to the latest scientific findings. 

How Insulin Works (or Doesn't Work)

Glucose, a type of sugar we get from the foods we eat, supplies energy to all our cells—muscle, skin, brain, etc. But it needs help getting from the digestive system into the bloodstream and then into the body’s various tissues and cells.

That’s where insulin comes in—the pancreas secretes this hormone when we ingest glucose and makes sure the glucose gets wherever it needs to go. Without insulin the body and its cells can’t survive. It plays a vital role in life, so clearly it’s a good thing to have.

But problems can occur when the body’s signaling for how much insulin the pancreas needs to produce goes awry, says Andrew van Eps, BVSc, PhD, MACVSc, Dipl. ACVIM, associate professor of equine musculoskeletal research at the University of Pennsylvania’s School of Veterinary Medicine, in Kennett Square. And, unfortunately, it is possible to have too much of a good thing.

Some people and horses are just born that way: They produce far more insulin than they need. In equids, Arabians, Morgans, ponies, and some Warmbloods might even carry a genetic risk for insulin overproduction, van Eps says. 

Others produce more insulin in response to glucose, he says, usually in association with obesity. The body becomes less sensitive to insulin, so it calls for more insulin to manage incoming glucose. Over time it keeps calling for greater quantities in a never-ending cycle of production increase. “That’s true insulin resistance (IR),” van Eps says. “The body keeps making more insulin to compensate for the fact that the insulin isn’t working well.”

Scientists classify insulin sensitivity and resistance as insulin dysregulation (ID). It’s important to study ID horses as one group, but it’s also important to recognize their distinctions, says Nicholas Frank, DVM, PhD, Dipl. ACVIM. Frank is associate dean for academic affairs and professor of large animal internal medicine at Tufts University’s Cummings School of Veterinary Medicine, in North Grafton, Massachusetts.

“You can’t assume you know why those insulin concentrations are high,” he says. “Certainly many of the horses that have high insulin concentrations have some degree of IR, but that might not be the whole picture.”


This article continues in the October 2017 issue of The Horse: Your Guide To Equine Health Care. Subscribe now and get an immediate download of this issue including this in-depth feature on how to manage the insulin resistant horse.

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About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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