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Insulin and Weight in Horses

Research shows that there is an association between obesity and high insulin, but obesity is the result, not the cause.
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There are many benefits to weight loss, and it should be aggressively pursued, but it won't make insulin resistance go away. Approximately 50% of horses with EMS are normal weight.

Easy keepers and overweight horses and ponies have been around forever. Laminitis has also always been with us, and it is no secret that overweight animals are at high risk. We now know that the vast majority of laminitis cases are caused by high insulin levels—hyperinsulinemia—associated with equine metabolic syndrome (EMS). Does this mean being overweight/obese causes insulin problems?

It might seem that way superficially, but the logic is faulty.

Many horses that develop laminitis are overweight or obese. We know that the vast majority of laminitis cases are caused by high insulin levels. The correlation has always been obvious, and it didn't take long for an assumption to arise that obesity is a laminitis risk factor and causes elevated insulin. There's just one thing: It's not true.

The 2015 Bamford study, published in the Equine Veterinary Journal, fed horses and ponies a control diet, or one designed to cause obesity by feeding either excess fat or excess fat and glucose. The weight gain did not reduce insulin sensitivity in either group. Dr. Nicholas James Bamford has also clearly shown that insulin responses to oral or intravenous glucose have marked variation by breed in horses of normal weight. You can read all of Dr. Bamford's work in detail in his thesis here: https://minerva-access.unimelb.edu.au/bitstream/handle/11343/148423/Bamford%20PhD%20Thesis.pdf?sequence=1.

Selim, et al., 2015, followed two groups of Finnhorse mares on either native pasture or intensively managed improved pasture. At the end of 98 days of grazing, the mares on improved pasture went from a body condition score of 5.5 to 7 and gained 145 pounds, but this was not associated with insulin resistance.

If obesity isn't a cause, why is more insulin resistance seen in obese horses, 25% to 50% of high-insulin horses, depending on the study, versus 10% to 15% of horses in general? The answer is simple. These horses are resistant to the effect of the hormone leptin, which results in increased appetite and weight gain. 

This is more than just splitting hairs. If you think obesity is a cause then weight control becomes a treatment, even possibly a cure. When you realize it is a consequence, not a cause, expectations for results of weight loss become more realistic. There are many benefits to weight loss, and it should be aggressively pursued, but it won't make insulin resistance go away. Approximately 50% of horses with EMS are normal weight.

For more background visit https://www.ecirhorse.org/ and see the ECIR Group films Diagnosis and Diet.

About ECIR Group Inc.

Started in 1999, the Equine Cushing's and Insulin Resistance Group, Inc. (ECIR Group) is the largest field-trial database for PPID and EMS in the world and provides the latest research, diagnosis and treatment information, in addition to dietary recommendations for horses with these conditions. Even universities do not and cannot compile and follow long term as many in-depth case histories of PPID/EMS horses as the ECIR Group.

In 2013 the Equine Cushing's and Insulin Resistance Group Inc., an Arizona nonprofit corporation, was approved as a 501(c)3 public charity. Tax deductible contributions and grants support ongoing research, education, and awareness of Equine Cushing's Disease/PPID and EMS.

The mission of the ECIR Group is to improve the welfare of equines with metabolic disorders via a unique interface between basic research and real-life clinical experience. Prevention of laminitis is the ultimate goal. The ECIR Group serves the scientific community, practicing clinicians, and owners by focusing on investigations most likely to quickly, immediately, and significantly benefit the welfare of the horse.

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This article was written by Eleanor M. Kellon, VMD.

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