Horse Illustrated Magazine

Q: I have a 17-year-old Mustang that came back high on the ACTH test for Cushing’s disease. She started Pergolide 5 days ago. I have her on grass hay. My question is about treats and supplements. Most pellets have alfalfa in them. What is safe to feed my horse?

A: Equine Cushing’s Disease, or pars intermedia dysfunction (PID), is a resultant condition from benign tumor growth in the pituitary gland. Seen mostly in older horses, this clinical syndrome manifests itself in the forms of hirsutism (excessive hair growth and inability to shed a winter coat) and laminitis, as the pituitary tumor secretes excess hormones that cause the adrenal glands to produce large quantities of cortisol, a steroid. Steroids do many things in the body but in excess, can cause havoc with everything from immune function to carbohydrate metabolism and insulin resistance. For this reason, Cushing’s horses are prone to laminitis, thus the need for dietary restriction of carbohydrates and sugars. Pergolide is a drug commonly used to help control Cushing’s disease. Acting on dopamine receptors in the brain, pergolide helps regulate the excess secretion of hormones and peptides from the pituitary gland that cause clinical signs of this disease.

Grass hay is the ideal forage for a Cushing’s horse, since it is low in soluble carbohydrates and sugars. Lush pasture access should be limited in these horses. In terms of complete feeds, there are a few brands that have emerged recently on the market specifically for horses with Cushing’s disease and its sister disease: equine metabolic syndrome – an umbrella term for horses that are overweight, insulin resistant, and hyperglycemic. These feeds are low in starches and sugars and high in fermentable fibers. All the major horse feed companies seem to have their own formulas now, including Purina Mills, Triple Crown Feeds, and Blue Seal. Molasses-free beet pulp is also ideal – having a low glycemic index and high in fiber, beet pulp can help bulk up a horse’s feed.

In terms of treats for a Cushinoid horse, your options are limited. Most commercial horse treats contain high sugar content because, after all, they are a treat. Even “natural” choices for treats such as carrots and apples shouldn’t be given to Cushinoid horses. Instead, try celery. If your horse sticks his nose up at this healthy suggestion, sugar-free candies such as what you would find in the diabetic aisle of your grocery store can also be given. Sugar-substitutes such as Nutrasweet and Splenda will not harm your horse in small quantities. Another suggestion is to try the lowest calorie treat of all: an extra scratch on the ear speaks as a reward as well!

— Anna O’Brien, DVM

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