Hyperinsulinemia in Horses: What to Watch For

Abnormal sweating, laminitis, cresty neck, and pot-belly weight gain were significant predictors of HI, researchers found.

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As they gain a better grasp of what to look for, veterinarians are diagnosing endocrinopathies (disorders of the endocrine system) in horses more frequently. Chances are, you’re already familiar with some of these diseases: The horse with pituitary pars intermedia dysfunction (PPID, or equine Cushing’s disease), for instance, probably has a shaggy coat, decreased muscle tone, and abnormal sweating. The horse with equine metabolic syndrome (EMS) likely has a cresty neck, fat buildups in abnormal places, and a predisposition for laminitis.

But do you know what a horse with another common endocrinopathy, hyperinsulinemia—HI, otherwise known as insulin resistance—looks like? If the answer is no, you’re not alone. Researchers are still in the process of learning what to watch for to suggest a horse has HI.

At the 2016 American College of Veterinary Internal Medicine Forum, held June 8-11 in Denver, Colorado, Steve Grubbs, DVM, PhD, Dipl. ACVIM, shared the results of a study in which he and colleagues examined the characteristics associated with HI in horses. Grubbs is the equine technical manager for Boehringer Ingelheim Vetmedica Inc., in St. Joseph, Missouri.

Specifically, Grubbs and his coworkers hoped to identify epidemiological characteristics of horses with hyperinsulinemia. Epidemiology simply refers to a study of the patterns, causes, and effects of health and disease conditions, along with risk factors and preventive approaches.

To accomplish this, they collected data on horses of varying ages, sexes, and breeds that exhibited at least one of the following clinical signs:

  • Hypertrichosis (abnormal hair growth);
  • Muscle wasting;
  • Abnormal fat distribution;
  • Lethargy;
  • Laminitis of unknown origin;
  • Increased water intake and urination (polydipsia and polyuria, respectively);
  • Susceptibility to infections; 
  • Abnormal sweating; and
  • Inappropriate lactation.

Grubbs said they did not include normal, healthy horses in the study.

A veterinarian examined each horse and collected blood to test the basal adrenocorticotropic hormone (ACTH, uncontrolled ACTH release can cause tissues to become insulin-resistant), fasting insulin, and glucose levels to determine whether the horse was hyperinsulinemic (HI+) or not (HI-). Then, the team evaluated the correlations between hyperinsulinemic horses and the clinical signs they displayed. Additionally, they paid close attention to whether horses tested positive or negative for PPID (PPID+ and PPID-, respectively).

Of the 504 horses included in the final data analysis, Grubbs and colleagues determined that 39% were HI+. They also confirmed that the older the horse, the more likely it is to be HI+ or PPID+/HI+.

Then the researchers looked specifically at HI+ horses, with or without PPID, to identify characteristics suggestive of disease development. They determined that:

  • Prevalence of HI was significantly greater among horses with cresty necks/fat pads and laminitis;
  • Horses with cresty necks were 2.3 times more likely to be diagnosed with HI than horses without cresty necks;
  • Horses with laminitis were 2.2 times more likely to have HI than horses without laminitis;
  • Horses with high glucose levels were 4.8 times more likely to have HI than horses with normal glucose levels;
  • Of the 504 enrolled horses, 61.9% were diagnosed with an endocrine disorder (PPID and/or hyperinsulinemia); and
  • 45% of PPID+ horses were also HI+.

“Based on the combined data of clinical signs, abnormal sweating, laminitis, cresty neck, and pot-belly weight gain were significant predictors of HI,” Grubbs said. “Therefore, when evaluating horses with suspected endocrine disease, at a minimum, ACTH, insulin, and glucose should be evaluated.”

Grubbs noted that additional long-term studies should be conducted in large populations of horses to better understand these equine endocrinopathies.

About the Author

Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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