Q. Can you provide more information on feeding the Cushing's horse? My dressage horse has Cushing's and is on cyproheptadine and Thyro-L, grass hay, and a quarter-cup of 10% sweet feed. I am worried he is not getting the essential vitamins.


A. The truly Cushingoid horse is glucose intolerant/ hyperinsulinemic (glucose concentrations in the blood can only be maintained by producing excessive amounts of insulin, which can affect bones and cartilage), increasing the risk for laminitis. He might also have increased needs for vitamin C secondary to the lack of cortisol control and resultant high plasma concentrations. Instead of sweet feed, use one of the higher-fat (up to 10-12%), high-fiber (greater than 10%) pelleted or extruded formulations now available. Feed only in amounts necessary to maintain good--but not fat--body condition. If he is on only a quarter-cup of the feed, I assume you are using it to administer the medications. You can get the same result by using a pelleted/extruded feed as described above and soaking it in water to form a mash that he would not be able to sort through to reject the medication powders.

Grass or grass/alfalfa mix hay is usually fine, but avoid hays harvested after a drought or a freeze--they tend to be higher in the soluble sugars than normal. If you are worried that the hay might be higher in sugar than normal, soak it in water for an hour before feeding to help reduce the sugar content.

If your horse has access to pasture, limit his grazing time to the morning hours and use a grazing muzzle if necessary to limit his intake. If the hay is of good quality or he has access to pasture, the only vitamins he might need are vitamin C (5-10 g twice a day) and vitamin E (500-100 IU/day), which can be found where horse supplements are sold. If you're still worried about vitamin intake, you could use one of the "complete" vitamin supplements in the recommended amounts, but do not over-supplement (vitamin toxicity can cause serious health problems)!

There are many misdiagnoses of "Cushing's" nowadays that are based solely on blood insulin response. If the horse is only hyperinsulinemic with normal pituitary function (normal plasma cortisol control), the vitamin C would not be necessary and perhaps be contraindicated. The other dietary recommendations would be the same. The fact that he is also on Thyro-L and is still in work as a dressage horse makes me wonder if he might fall more into the category of just insulin-resistant than true Cushing's.

About the Author

Sarah Ralston, VMD, PhD, Dipl. ACVN

Sarah L. Ralston, VMD, PhD, Dipl. ACVN, is a professor in the Department of Animal Sciences at Rutgers' School of Environmental and Biological Sciences, specializing in equine nutrition. Her research has focused on the effects of diet on metabolism, behavior, and the development of orthopedic disease in young horses, and she has additional interests in nutritional modulation of stress, metabonomics (the study of metabolic responses to drugs, environmental changes, and diseases), and pasture management. Previous research highlights were the pioneering work she did in nutrition for geriatric horses and post-surgical colics while at Colorado State University in the 1980s and the discovery of the correlation of hyperinsulinemia with development of osteochondrosis in young Standardbreds.

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