AAEP Convention 2004: Horseman's Day--Cushings

Christy Malazdrewich, DVM, MVSc, PhD, Dipl. ACVIM, assistant clinical professor at the University of Minnesota, discussed metabolic problems at Horseman's Day at the 50th annual American Association of Equine Practitioners (AAEP) Convention in Denver, Colo., Dec. 4-8, 2004. She gave clear-cut descriptions of two baffling conditions--Cushing's disease and metabolic syndrome. She opened with this explanation: "Although the two disorders feature some striking clinical similarities--most notably a predisposition to development of chronic laminitis--the underlying disease biology is quite different in each case and successful management requires that the equine veterinarian distinguish between them."

She first dealt with Cushing's disease--a disorder of the pituitary gland that results in hormonal imbalances. These imbalances result in a variety of clinical signs including:

  • A long, wavy hair-coat that fails to shed according to normal seasonal patterns;
  • Excessive sweating;
  • Lethargy;
  • Poor athletic performance;
  • Chronic recurrent laminitis;
  • Infertility;
  • Weight loss;
  • Muscle wasting;
  • Passage of large amounts of urine;
  • Delayed wound healing; and
  • Increased susceptibility to infections.

The disease tends to occur in middle-aged to geriatric horses, with an average age of approximately 20 years at the time of diagnosis. In many cases, she said, diagnosis of the disease can be made via outward manifestations, but in others an endocrinologic test might be required. Two primary tests are in use today--one is the dexamethasone suppression test, and the other is a test that measures the level of a hormone produced by the pituitary gland (ACTH).

Malazdrewich then turned to treatment protocols for Cushing's. She had this to say: "Optimal management of Cushing's disease involves a combination of both specific medication to normalize the function of the pituitary gland and supportive care to address and prevent complications associated with the disease. In both cases, management will be life-long as there is no way to reverse the disease process. In the early stages, specific medication may not be required and conservative measures such as body clipping to remove the long hair coat, strict attention to diet, and scrupulous attention to teeth, hooves, and preventive care may be sufficient to provide good quality of life. If affected insulin resistant, sweet feed and other feedstuffs high in soluble carbohydrates should be avoided in favor of diets emphasizing fiber and fat. In both mildly and severely affected horses, the importance of early diagnosis and aggressive treatment of  bacterial infections cannot be overstated."

Two drugs have been used with some success to treat the disease, she told her listeners. One is pergolide, which acts on the pituitary to reduce the amount of hormones secreted. The second is cyproheptadine, which suppresses undue releases of cortisone by the adrenal glands.

Pergolide is administered orally on a daily basis in a syrup form. Cyproheptadine is given daily, but comes in a tablet form.

Malazdrewich then turned to a discussion of metabolic syndrome (MS), a condition that often is first recognized when chronic recurrent laminitis becomes evident in fat horses lacking other foundation triggers.

"Obesity," said Malazdrewich, "appears to be the central problem in both humans and horses suffering from metabolic syndrome. Although body fat is commonly viewed as an inert substance that functions solely as a storage form of energy, nothing could be further from the truth. Body fat, especially that stored in the abdomen, liver, and skeletal muscle, contains cells that are very active metabolically and hormonally, and when present in excessive amounts their effects can trigger a cascade of metabolic disturbances leading to insulin resistance and persistent hyperglycemia (high blood sugar)."

Younger horses, when compared to those with Cushing's, develop metabolic syndrome if they are obese. Cases have been reported in horses 10 and under. And, she added, horses suffering from metabolic syndrome normally have nothing wrong with the pituitary gland.

"At present," said Malazdrewich, "treatment strategies for equine metabolic syndrome focus almost exclusively on reversal of obesity and insulin resistance through strict dietary modification and implementation of an exercise program, if possible. Of course, horses suffering active bouts of laminitis cannot be exercised until founder has been brought under satisfactory control."

She noted that the most important aspect in the feeding of affected horses involves strict limitation of soluble carbohydrates in the diet--all grains and sweet feeds. The diet, she said, should have at its base good quality grass hay.

There are many unanswered questions with regard to metabolic syndrome. She said: "Very little scientific work has been on the condition at this point, and although there are some parallels with the human disorder called metabolic syndrome, it is still very unclear how deep those similarities go."

One of the drawbacks in dealing with MS, she said, is the fact that there is "not a whole lot of scientific evidence available."

About the Author

Les Sellnow

Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.

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