Equine Metabolic Syndrome (EMS)

Feeds and Feeding Horses with Equine Metabolic Syndrome (EMS)

What is Equine Metabolic Syndrome in horses

Equine Metabolic Syndrome (EMS) is the name that has been adopted to describe conditions including peripheral Cushing's syndrome, pseudo-Cushing's syndrome, hypothyroidism, and insulin resistance. Less common names included omental Cushing's syndrome or central obesity.

EMS is a term used to describe a condition in horses that is essentially caused by insulin resistance. Insulin is a hormone produced by the pancreas to control blood glucose levels. When feed that contains non-structural carbohydrates like simple sugars or starch (see below for more detail on non-structural carbohydrates, (NSC) are eaten, they are digested and absorbed into the blood as glucose. When glucose enters the blood, insulin is released to signal to the horses muscle and liver cells that they should absorb the glucose. Once glucose is absorbed and the glucose concentration in the blood drops back to baseline (normal) levels, the insulin is broken down and insulin levels also return to normal.

Insulin resistance occurs when a horse's liver and muscle cells do not respond to insulin and don't absorb the glucose. The horse keeps producing more and more insulin to try and get the message across to the muscle and liver. The resultant insulin resistant horse, has higher than normal levels of blood insulin and glucose after they have eaten a meal that contains NSC (also known as insulin spikes).

How do I know my horse has Equine Metabolic Syndrome

Horses with EMS tend to be 'easy keepers' and are often overweight or obese, sometimes with patchy fatty deposits over their neck, shoulders and rump. This fat/obese state is probably what causes the insulin resistance in these horses.

The most serious complication for a horse with EMS is laminitis. It has long been known that overweight horses and ponies were at an increased risk of laminitis; however the exact mechanism was unknown. Recent research conducted at the University of Queensland by Asplin et al. has shown that prolonged elevated insulin levels can cause laminitis in otherwise normal horses. Thus horses with EMS and the associated insulin resistance are prone to insulin induced laminitis.

Horses with Cushing's disease typically display insulin resistance and are thus also considered in the Equine Metabolic Syndrome category. Like horses with insulin resistance, horses with Cushing's disease are also very prone to laminitis.

What causes Equine Metabolic Syndrome in horses

With the exception of horses with Cushing's disease, horses with EMS are normally overweight, thus their intake of calories needs to be carefully managed in order to prevent additional weight gain and hopefully encourage some weight loss (which can be achieved when a diet is combined with daily exercise).

A horse with EMS must have their intake of NSC carefully controlled in order to prevent spikes in blood insulin levels. Failure to control blood insulin levels through careful management of the diet can and often does lead to laminitis in EMS affected horses.

What are Non-Structural Carbohydrates?

Non-Structural Carbohydrates (NSC) include glucose, sucrose, fructose, starch and fructan. With the exception of fructan, non-structural carbohydrates are digested in the horse's small intestine and absorbed into the blood as glucose. Once this glucose is absorbed it triggers the release of insulin in the blood. In insulin resistant horses, it is the non-structural carbohydrates that lead to high levels of blood insulin, which can in-turn lead to laminitis in susceptible horses.
NSC are present in large quantities in cereal grains like oats, corn, barley and sorghum, in molasses and in by-product feeds like rice bran, wheat bran and pollard. They can also be present in large amounts in some pastures and hays, especially rye grass and oat forage.

NSC = starch +water soluble carbohydrate (WSC)

What level of Non-Structural Carbohydrate is safe?

The 'safe' level of non-structural carbohydrates for equines has not been scientifically determined and it appears it does vary on a case by case basis for horses affected by EMS. However, field data suggests that horses with EMS should be maintained on a diet that contains non-structural carbohydrate content less than 12% and preferably less than 10% on average per feed.

Feeding feeds with non-structural carbohydrate levels above 10% - 12% may exacerbate EMS and could lead to a bout of laminitis in susceptible horses.

How diet helps Equine Metabolic Syndrome or Dysbiosis in horses

Selecting suitable feeds for a horse affected by EMS is not an easy task. Forages vary dramatically in the level of NSC they contain, with forages like ryegrass and oat hay capable of having NSC 30%. Weather damaged Lucerne hay and stemmy, mature pasture hay are most likely to contain suitably low levels of non-structural carbohydrates. Grain can contain NSC content over 60%. To be certain that the forage the horse has access to, is suitable, you should have the NSC content tested. For information on how to do this, see www.dairyone.com

The level of NSC in commercial feeds is also highly variable, making it difficult for owners of EMS horses to select a suitable supplementary feed. You should ask for the NSC content of all feeds before feeding.

Only feeds with < 12% NSC should be considered for horses susceptible to EMS. When you have selected a suitable feed, it should be introduced into your horse's diet slowly, as some EMS horses are extremely sensitive and will still react to a feed, even though it may seem suitable. It is also important to feed little and often to avoid insulin spikes associated with the expectation of feeding.

Equine Metabolic Syndrome is characterised mostly by insulin resistance, as the affected horse has high levels of blood glucose and insulin, caused primarily by feeding high NSC diets, and under work. Selecting suitable feeds for EMS horses requires a sound knowledge of the NSC content of all the feed eaten, including the treats such as molasses.

Key Points

  • EMS describes the metabolic disorders that are attributed to insulin resistance in horses. Horses with EMS (which includes horses with Cushing's disease) are especially prone to laminitis.
  • 'Non-structural carbohydrate, NSC' is the term used to describe the readily available sugar and starch levels in horse feeds.
  • When a horse eats NSC blood glucose and insulin levels increase.
  • Insulin resistance in EMS horses causes the abnormally high blood insulin levels.
  • These high levels of insulin can lead to laminitis.
  • For horses with EMS, feeds with <12% NSC should be selected to control blood insulin levels and reduce the risk of laminitis developing.