Equine Metabolic Syndrome vs Equine Cushing’s Disease

Written by: Amber Long, West Bladen High School FFA President

 

Equine Metabolic Syndrome

Equine Metabolic Syndrome (EMS), or Insulin Resistance, is a disorder of carbohydrate metabolism that is usually seen in overweight, middle-aged horses. It is associated with severe laminitis. These horses may build up a high level of cortisol. Increased circulating levels of cortisol increase blood sugar and inhibit the uptake of glucose into cells by antagonizing the action of insulin. Persistent high blood sugar is known to be toxic and it is possible that it contributes to laminitis in horses by damaging the blood vessels in the hoof.

Clinical signs include:

•  Laminitis – typically begins in the spring with rapid growth of grass 
•  General obesity with regional and/or regional adiposity 
•  Crusty neck, fat deposits around the tail head, sheath and suborbital fossa (hollow above the eyes), occasional subcutaneous masses on the trunk

Resting insulin and blood sugar are the most common screening tests used to diagnose the metabolic syndrome. If you suspect that your horse has laminitis due to metabolic syndrome, schedule a physical exam with your veterinarian. You may also test your hay to determine the carbohydrate content. Straight alfalfa is not appropriate for these horses.

The goal of treatment is to improve insulin sensitivity and raise the threshold for laminitis. Metabolic Syndrome can be managed through diet and exercise.

Equine Cushing’s Disease

Equine Cushing’s disease is a disorder of the pituitary gland that results in hormonal imbalances. In affected horses, the pituitary gland is usually enlarged and overactive as a result of faulty regulation by the hypothalamus. This disease usually occurs in middle-aged and geriatric horses.

Clinical signs include:

•  A long, wavy hair coat that fails to shed according to normal seasonal patterns 
•  Excessive sweating 
•  Lethargy and poor athletic performance 
•  Chronic recurrent laminitis 
•  Infertility 
•  Weight loss 
•  Muscle wasting, especially along the topline 
•  Abnormal distribution of fat, with accumulations in the crest of the neck, tail head, sheath, and above the eyes 
•  Consumption of large volumes of water and passage of large amounts of urine 
•  Delayed wound healing 
• Increased susceptibility to infections

In advanced cases, diagnosis is straightforward. However, diagnosis of early cases or those with few obvious clinical signs is more difficult. Two commonly used tests are: the dexamethasone suppression test and measurement of plasma ACTH concentration.

Managing Cushing’s disease involves both specific medication to normalize the function of the pituitary gland and supportive care to address and prevent complications associated with the disease. Management will be life-long because there is no way to reverse the disease process.

For additional information, visit these articles: Equine Endocrinology: Cushing’s Disease and Metabolic Syndrome from the American Association of Equine Practitioners, Insulin resistance in horses from University of Minnesota Extension, and Management of Equine Cushing’s Disease and Equine Metabolic Syndrome from the University of Florida.