Insulin Resistance: Hold the Grain, Please

Management of insulin resistance might lower the risk of laminitis, and one of the cornerstones of management is diet. “Think of these horses as being in a prediabetic state,” said Nicholas Frank, DVM, PhD, Dipl. ACVIM, associate professor of large animal clinical sciences at the University of Tennessee, at the 2006 AAEP Convention. “They need to exercise more and take in less sugar.”

He made these recommendations:

  • Take obese horses off sweet feed, they don't need it anyway.
  • Consider a grazing muzzle.
  • Don’t overfeed them.
  • Feed hay lower in nonstructural carbohydrates (NSC; forage testing labs can tell you a hay’s NSC content).
  • Induce weight loss by feeding hay initially at 2% of the horse’s current body weight, decreasing to 1.5% of current body weight, then finally dropping to 1.5% of ideal body weight.
  • Consider pergolide treatment in horses with EMS to stave off PPID.
  • Exercise horses to decrease weight.

If an insulin-resistant horse develops laminitis, Frank recommended the following management practices:

  • Take the horse off pasture entirely--remove some horses permanently, but most temporarily.
  • Keep the horse in a dry lot.
  • Hand-walk him for exercise once his feet are stabilized.
  • If he's obese, feed low-sugar hay.
  • If he’s lean, feed hay plus a low-NSC feed.

Consider strategic use of levothyroxine (generally used as replacement therapy in reduced or absent thyroid function) for three to six months in obese horses.

However, “We are not treating hypothyroidism!” he stated. “That condition is extremely rare in horses. We are using it to accelerate metabolism (to decrease body weight).” Frank said in an ongoing study, horses in a dry lot and given levothyroxine (Thyro- L; Lloyd Inc., Shenandoah, Iowa) lost an average of 62 kg, compared to 25 kg lost by horses in a dry lot without evothyroxine.

The following facts should be considered if you have a horse that is showing signs of becoming overweight or having insulin resistance.

  • Not all obese horses have EMS, and not all horses with EMS are obese.
  • Diet and exercise are the main management and prevention strategies. Owners should avoid feeding concentrates and control affected or at-risk horses’ exposure to pasture.
  • Levothyroxine can be given to reduce body weight and increase insulin sensitivity for three to six months.

Get research and health news from the American Association of Equine Practitioners 2006 Convention in The Horse's AAEP 2006 Wrap-Up sponsored by OCD Equine. Files are available as free PDF downloads.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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