With prompt diagnosis, drug therapy with regular blood work to check dosage, and a well-managed diet, many horses with PPID can enjoy many happy and active years. | Photo: iStock

Q: My veterinarian is concerned that my 22-year-old gelding might have metabolic issues, so we tested him for Cushing’s and insulin resistance. We just got the results back and his ACTH was close to 150 pg/ml (normal range 9 to 35) and his insulin was 45 uIU/ml (normal 10 to 40). We will be starting him on pergolide, but I would like to know how I should manage his diet. What suggestions do you have?

A: In the fall, measuring a horses adrenocorticotropic hormone (ACTH) levels is often used as a diagnostic tool for pituitary pars intermedia dysfunction (PPID, also known as equine Cushing’s disease). It peaks between mid-August to mid-October as part of the metabolic preparation for winter and results in levels anywhere up to about three times those found at other times of the year. It used to be thought that this made early fall a poor time of year to use ACTH levels as a diagnostic tool. However, in recent years, research has shown that horses with PPID have a seasonal rise that is even higher than unaffected horses. Contrary to previous belief this might in fact make fall a good time of year to test due to the potential for a more profound response to the seasonal ACTH rise in horses with PPID.

Disease Overview

The pituitary tumors associated with PPID influences the adrenal glands to release cortisol, a stress-related hormone. Cortisol plays an important role in the metabolism of carbohydrates, proteins, and fats and helps to balance the effects of insulin in the breakdown of sugar for energy. It is a vitally important hormone; however, when elevated for extended periods, as in the case of high circulating ACTH, high cortisol levels could have some negative consequences. These include inducing a degree of insulin resistance (IR), muscle wasting, a pot-belly appearance, immune deficiency, and an increased susceptibility to