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Equine Metabolic Syndrome

What is Equine Metabolic Syndrome?                                                  

The term Equine Metabolic Syndrome (EMS) is used to signify the condition in horses in which all three of the following exist:

  • Insulin resistance (IR)
  • Laminitis – may be severe, acute or low-grade and chronic
  • Regional fat deposition in the form of a “cresty” neck or enlarged fat pads

These horses are usually described as “easy keepers” by their owners and often have fat deposits in the crest of the neck, over the tail head, above the eyes, behind the shoulders, and in the sheath of male horses. They may be obese overall or simply have regional fat deposition as previously described.  These horses used to be categorized as “hypothyroid,” however it has been shown that removing the thyroid gland of a horse does not result in laminitis. We now know that low concentrations of thyroid hormones in the blood of horses with EMS are a secondary consequence rather than primary cause of the metabolic condition.

What is Insulin Resistance? IR is defined as the failure of tissues to respond normally to the hormone, insulin. Insulin is one of the hormones responsible for maintaining normal blood glucose levels. Insulin is released by the pancreas when blood glucose levels are high, stimulating the body’s cells to take up glucose from the blood stream. This is not dissimilar to humans with Type 2 diabetes. IR horses are predisposed to laminitis.

IR diagnosis: IR is typically diagnosed by measuring insulin levels in the bloodstream. False negative results are possible in very mild or early cases of IR. Insulin resistant horses have elevated resting insulin levels because the cells are not responding to it and the body thinks it needs to pump more out. Horses should not be fed grain for at least 4 hours before the blood sample is taken. Sometimes more extensive testing is performed if your horse has the typical clinical signs of IR but his resting insulin levels are normal.

How is EMS different from Equine Cushings Disease? Horses with EMS do not necessarily have dysfunction of the pituitary gland, which is the hallmark of Equine Cushings Disease. In fact, the recognition of EMS developed from the increased recognition of horses with chronic laminitis that consistently tested negative for ECD. It is possible that a horse with ECD could also have IR, laminitis and some of the physical attributes such as a cresty neck or regional fat deposition. Horses with EMS and a negative Cushings test do not benefit from treatment with pergolide.

Treating EMS and IR: The two most important aspects to managing EMS are nutrition and exercise. Your veterinarian can guide you through this process. A low starch (<10-12% non-structural carbohydrate) diet and daily exercise should be instituted immediately as long as the horse is not lame. Overweight horses with active laminitis that are unable to be exercised due to lameness must be kept on a strict diet to avoid overfeeding. These horses may benefit from a temporary course of levothyroxine (Thyro-L) to help accelerate weight loss and help sensitize the cells to insulin. Once these horses are sound enough to start an exercise program or once the ideal weight has been obtained they should be weaned off of the medication. Check out Feeding the Metabolic Horse for more information.