Equine Metabolic Syndrome

Equine Metabolic Syndrome (EMS), previously known as Peripheral Cushing’s Disease, is a hormonal disorder of horses, and more commonly ponies that has been identified in the recent past.  It has some similarities with Cushing’s Disease, most notably in its propensity to cause laminitis.  Overweight native ponies are most frequently affected, although it has been observed in all breeds and types.  There is also a strong link with obesity – any pony can be affected by EMS, but it is observed far more frequently in overweight animals.

The primary disorder in EMS is insulin resistance.  The role of insulin within the body is to enhance the uptake of glucose from the bloodstream into cells, and in conjunction with glucagon plays the major part in regulating blood sugar levels.  Ponies with EMS do not respond to insulin as they should, so glucose remains within the bloodstream.  This is very similar to type II diabetes in humans.  There are also some abnormalities in fat metabolism that can contribute to the disease – firstly, the production of steroid-like hormones by fat, and secondly the conversion of inactive steroid hormone (cortisone) back to its active state (cortisol).  This leads to a higher than normal circulating steroid hormone circulation, similar to Equine Cushing’s Disease.

Clinical Signs

  • Laminitis
    • The reason why EMS causes laminitis is currently the focus of much research.
    • In humans, high insulin levels have been associated with blood vessel narrowing and damage, and a heightened inflammatory state, which may be the cause of laminitis in ponies with EMS.
  • Abnormal Fat Deposits
    • Typically seen as extremely large deposits above the eyes, in the neck and crest, behind the shoulder and at the tail head.
  • Difficulty in weight loss
  • Obesity
  • Lethargy
  • Excessive drinking and urination


The diagnosis of EMS revolves around clinical signs, in combination with blood testing.  Typically, samples are taken for insulin and glucose, and sometimes triglyceride (a component of fat) levels.  High levels of insulin and glucose are seen in ponies with EMS.  In some cases, EMS can be present with normal blood results.  These ponies require dynamic testing, where their response to glucose is measured.


By far the most important treatment for Equine Metabolic Syndrome is diet and exercise.  The diet must be well balanced, containing all essential vitamins and minerals, and contain low levels of soluble carbohydrate.  This is typically achieved by feeding soaked hay with a low-calorie balancer (e.g. Bailey’s Lo-Cal Balancer).  Ponies suffering from laminitis are often also supplemented with biotin and methionine, which are essential for proper hoof growth.  Some research has shown a benefit to anti-oxidants in the diet, and supplementation with Vitamin E and Chromium can be helpful.  An absolute level of Chromium to supplement has not been determined, but it is currently recommended that Vitamin E is provided at a level of 8,000 – 10,000 IU (International Units) per day.  More information on feeding the metabolic horse and pony can be found here.

Exercise is also absolutely vital for horses with Equine Metabolic Syndrome (EMS) These ponies are naturally resistant to insulin, so cannot take glucose into their muscles properly.  Exercise has been shown to significantly improve the uptake of glucose by muscles, and reduce blood sugar levels.  Obviously in ponies suffering from laminitis this will not be immediately possible, so in these cases we use medical therapy to give the same effect as exercise.

Metformin is a human drug, known as an oral hypoglycaemic.  Its effects are much the same as exercise, in that it allows muscle cells to uptake glucose independent of insulin.  Recent research has shown that to have constant effective levels of the drug, it should be dosed three times daily, although in the past we have had some good results with twice daily dosing.  Fortunately, metformin is also a relatively inexpensive drug, which makes its use in managing EMS ponies with active laminitis not only vital, but also affordable.  It should not be seen as a long term treatment – once it is possible then it should be replaced with exercise. It is relatively unpalatable and can be difficult to get ponies to eat because of its “sweaty-sock” taste!!

Some recent research has also suggested that ponies with EMS may benefit from treatment with Trilostane (Vetoryl).  This drug inhibits an enzyme involved in the production of steroid hormone, and has been previously used in the treatment of Cushings Disease in both horses and dogs.  Ponies with EMS can have problems with increased steroid concentration due to abnormal fat metabolism, and inhibition of this abnormal metabolism appears to have some benefits.

In the USA, many ponies with EMS are treated with thyroid hormone to speed weight loss.  Thyroid hormone in appropriate size oral doses for the horse is not available in this country at the moment, and it is the opinion of many that diet, exercise and where appropriate, metformin, is perfectly adequate for EMS treatment.  Recent studies have also shown that thyroid hormone increases glucose absorption from the small intestine, which is in fact the opposite of what we are trying to achieve.


The major threat to ponies with Equine Metabolic Syndrome EMS is laminitis, and the majority of cases we diagnose will be suffering at the time of diagnosis.  As long as recovery from the laminitis is achieved, then with appropriate diet and exercise the prognosis for Equine Metabolic Syndrome is good.