Endocrine Disorders in Horses

December 31, 2007 (published) | September 22, 2014 (revised)

The two most common hormonal disorders in horses are Cushing’s disease, correctly called PPID, and insulin resistance or insulin dysregulation, which is the same as equine metabolic syndrome.  Both of these diseases are extremely important because either of them can lead to laminitis and founder. In one study, 22% of horses over the age of 15 were determined to have PPID and 32% were determined to have insulin dysregulation. Insulin deregulation is more common in ponies, Morgans and Arabians, and if possible it is critical to diagnose these diseases before a horse founders. The best method of diagnosing insulin dysregulation is by giving the horse a dose of corn syrup and checking an insulin level 60 and 90 minutes later. Horses that are insulin resistant should be fed hay only plus a ration balancer. Hay should be fed at about 15 pounds per day for a 1,000-pound horse, and if the hay has greater than 10% nonstructural carbohydrates, it should be soaked for 60 minutes before feeding. 

Some horses require thyroid hormone supplementation to lose weight quickly and prevent founder. Horses with PPID or Cushing’s disease may be overweight, have abnormal hair coats and drink lots of water. Any older horses should be tested with a blood sample to determine if the horse has either disease. Treatment Cushing’s is treatable, but early diagnosis is critical to prevent laminitis.  If you have a horse over 15 years old, ask your veterinarian about testing for Cushing’s disease and insulin dysregulation. If we can start catching these diseases before laminitis and founder develop, it will save the horses from the painful condition of laminitis and save owners a lot of money.

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