In order to provide complete functionality, this web site needs your explicit consent to store browser cookies. If you don't allow cookies, you may not be able to use certain features of the web site. It is recommended that you allow all cookies.

Equine Metabolic Syndrome (EMS)

This condition describes horses that are obese, have insulin resistance due to increased tissue production of cortisol, and have recurrent laminitis. The disease has received different names in the past, particularly Peripheral Cushings Syndrome, but the most appropriate term is Equine Metabolic Syndrome (EMS).

In the past it was common for horses suffering from EMS to be diagnosed with hypothyroidism (under-working thyroid gland). However, in experimental studies that have been undertaken, neither obesity nor laminitis develops in adult horses from which the thyroid gland has been removed.

Certain management practices tend to promote the development of obesity in mature horses. These management practices include the provision of grain and fat rich rations to healthy horses that are relatively inactive.

Some horse breeds and ponies appear to be genetically predisposed to this condition.

The exact cause is still unknown and there is ongoing work to try to find the connection between obesity and the development of laminitis. What is known so far is that horses affected with obesity-associated laminitis are insulin resistant and are commonly glucose (sugar) intolerant.

As previously explained the specific mechanisms responsible for the development of insulin resistance are not fully understood. It is believed that metabolically active substances are released from fatty tissue that interferes with the action of the insulin. Fatty cells, particularly in the abdominal cavity, produce an enzyme that converts plentiful circulating cortisone into active cortisol. This cortisol could also contribute to insulin resistance.

Insulin resistance tends to be associated with an increase in blood glucose and damage to the blood vessels has been directly attributed to elevated blood glucose levels. This is important because laminitis arises from abnormalities in the regulation of blood flow to the hoof.

In summary, obese horses have altered blood flow to the hoof leading to laminitis which results from dysfunction of the blood vessels arising from insulin resistance.

Horses affected with EMS are typically aged between 8 and 18 years and pony breeds appear to be predisposed to this condition. Horses presented for treatment of laminitis often show subtle signs, and a specific, clearly evident causative factor, cannot be identified in the history. The degree of pain associated with laminitis in these horses is often, but not necessarily, mild.

Your vet will perform a physical examination of the affected feet; this commonly reveals evidence of chronic laminitis – dropped sole, divergent growth lines on the hoof wall and widening of the white line zone. Radiographs (x-rays) of the feet may be necessary to assess the severity of the laminitis. Radiographic findings may include evidence of pedal bone rotation or pedal bone remodelling.

Horses affected by EMS are often characterised as being overweight or obese. These horses are often referred to as good doers, and most horse owners frequently report that it is very difficult to reduce the weight of these horses by dietary restriction.

The exterior distribution of body fat in these obese horses commonly includes the neck (cresty neck), the rump and the tail head, but most affected horses tend to be distinctly overweight generally. Affected geldings often develop a swollen sheath. Affected brood mares sometimes exhibit abnormal oestrous cycling.

A diagnosis of EMS can be suspected based on the clinical signs of obesity and laminitis. However your vet may elect to perform some further diagnostic tests, particularly through different blood samples to confirm the diagnosis. The blood glucose (sugar) concentration may be normal or elevated in affected horses. Serum insulin and free fatty acid concentrations are commonly elevated. Ideally assessment of both glucose and insulin should be made on a fasted animal to eliminate variability associated with digestion.

You vet may also want to perform more advanced blood tests that will require administration of glucose in the vein or orally and insulin to your horse, and then obtaining a number of  blood samples over the following hours. This is known as either an intravenous or an oral glucose tolerance test.

Feeding growing and mature horses and ponies rations high in grain should be discouraged. Careful attention to ration formulation should include consideration of the size of the horse and the level of physical activity. Many horses develop obesity because they are fed too much grain. The most effective preventive and treatment measures are those associated with both increased physical activity and dietary weight reduction.

Increased exercise has been shown to improve insulin sensitivity. In horses affected with laminitis, increased activity intended to facilitate weight reduction might be detrimental until the laminitis has been considered less painful.

Recently introduced anti-diabetic (insulin sensitizing) drugs that increase the action of insulin in peripheral tissues can also be used; however these are no substitute to diet restriction and increased physical activity.