Introduction to Equine Metabolic Syndrome (EMS)

What is EMS?

Equine metabolic syndrome (EMS) is a hormonal condition, previously termed peripheral cushingoid syndrome, pre-laminitic syndrome and syndrome X, which has similarities to diabetes in humans. It is a complex, multi-factorial condition associated with an increase in susceptibility to laminitis.

What causes EMS?

EMS may be caused by an inappropriate diet, lack of exercise or obesity.  Fat cells can produce high levels of a particular hormone, cortisol.  Obese horses often have persistently high levels of cortisol that result in chronically high blood glucose levels, which in turn stimulates the production of insulin.  Insulin would usually work by encouraging the body’s cells to take up glucose from the blood and either store it or use it as an energy source.  Horses with EMS become “insulin resistant” and end up with constantly high levels of insulin and glucose in their blood.  This has numerous effects within the body, one of which is to cause damage to the blood vessels in the hoof, resulting in laminitis.  Although it is seen in many breeds of horses, EMS seems to affect certain breeds more than others, such as British native ponies. Horses that are considered to be ‘good doers’ may be more susceptible to EMS if they become overweight.

What are the clinical signs of EMS?

EMS is diagnosed by taking a complete history, performing a physical examination and taking blood samples. One or more of the following symptoms are typical of EMS:

• Obesity or presence of abnormal fat deposits in specific areas of the body such as the crest of the neck, base of the tail or behind the shoulder.
• Increased susceptibility to laminitis.
• Lethargy, increased drinking (polydipsia) and increased urination (polyuria).

Fat deposits may also occur in horses that are not overweight.  Fat deposits and laminitis are also seen with Cushing ’s disease, so this should also be considered when these signs are present. However, EMS is generally diagnosed in horses of any age, whereas Cushing’s Disease is usually seen in older animals and is often associated with changes to the coat.

How can I prevent or manage EMS?

The prevention and management of EMS is very similar to laminitis. As fat produces some of the hormones involved in EMS, an appropriate diet and suitable exercise regime should help to reduce the risk of your horse developing EMS, find out more – feeding horses with EMS. Feed smaller quantities or low calorie foodstuff and limit grazing to help weight loss and prevent future weight gain. Adding antioxidants, such as vitamin E, to the diet may be beneficial and early reports suggest that manganese may improve the activity of insulin.  Soaking hay will decrease sugar levels and calorie content. Putting hay inside a double haynet (i.e. one haynet inside another) or in a small‑holed haynet will slow down feeding. If laminitis is not a risk, then daily exercise will help your horse lose weight and may increase insulin sensitivity. Regularly monitoring your horse’s weight using body condition scoring and a weigh tape is recommended.

How is EMS treated?

EMS can usually be managed by controlling your horse’s diet and having an effective exercise regime. Medical treatment for EMS is still being researched. A small study has shown the human medicine, metformin, to be safe and effective in reducing insulin and glucose levels. However, more research is needed to confirm these findings.  Horses suffering from acute laminitis should be treated appropriately and only exercised following discussion with your vet.

What is the prognosis for EMS?

In most cases, EMS is a reversible condition that can be managed and resolved with an appropriate diet and exercise regime, although those animals that have suffered from laminitis may require ongoing remedial farriery.

Thank you to vets, Rick Farr and Nikki Pursey, of Farr & Pursey Equine Veterinary Services, for their input to this article.

Helpful resources

Liphook Equine Hospital and Laboratory – Equine Metabolic Syndrome