Question

Ruby is my 24-year-old Quarter Horse mare. She weighs about 1,000 lb (450 kg), and she’s in moderate body condition. She has insulin dysregulation and Cushing’s disease. She’s rehabbing from an injury, so she’s in her stall all but six or seven hours a week. She consumes about 16 lb (7 kg) of hay per day; most of the hay is timothy, though there is some alfalfa and orchardgrass in it. She is fed 5 lb (2.3 kg) of an easy-keeper feed per day, and I supplement ground flaxseed, salt, natural-source vitamin E, and a digestive aid. She also receives pergolide. I am happy with her weight, but ever since I started the pergolide, she is picky, sometimes not finishing her grain. I want her to have the best diet possible given her health issues.

Answer

Low-level inappetence is not unusual in horses given pergolide, the most prescribed medication for pituitary pars intermedia dysfunction (PPID, formerly known as Cushing’s). The medication slows the progression of the disease and reduces clinical signs. In one study, researchers observed that 32% of horses given pergolide had inappetence.^*

Switching Ruby to a different feed may help in this situation if her appetite issues have been going on for a while. The current feed appears to be relatively low in calories and nonstructural carbohydrates (NSC). Feeds designed to be low in calories and NSC often contain high-fiber ingredients that are less palatable to horses. Your horse may find a different feed more palatable depending on the ingredients. Another option might be to transition to a ration balancer without concerns about weight loss, especially if you can increase the amount of hay offered to provide additional calories.

A ration balancer may have slightly higher NSC levels than the current feed, but it would be fed at 1.5-2 lb (0.7-0.9 kg) per day, so the total amount of NSC would be similar, if not lower, making it a suitable option for horses with insulin dysregulation.

Being able to increase the amount of hay provided is also beneficial to overall health and wellness, as it increases time spent eating. Even though you don’t mention a hay analysis, I assume Ruby is doing well on the current hay, so an increase in hay (a couple of pounds per day) is not a concern. However, if you have recurring issues with managing her insulin levels, then I recommend evaluating the amount of starch and sugar in the hay to make sure it is suitable for her.

^*Wright, A.M. 2009. Pharmacokinetics of pergolide in normal mares. Kansas State University. p. 55.