EMS: My horse has Equine Metabolic Syndrome…what to do?

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EMS: My horse has Equine Metabolic Syndrome…what to do?

What is EMS?

Equine metabolic syndrome (EMS) can lead to a number of other issues with your horse including laminitis that can be traced back to insulin dysregulation (ID – or Insulin Resistance – IR). Also, as horses age they’re at an increased risk developing Pituitary Pars intermedia Dysfunction (PPID) which also may impact their weight and general health.

But WHY?

Similar to humans with type 2 diabetes, horses tend to exhibit many of the same symptoms when they have insulin resistance (e.g. obesity). Also like humans, there is likely a genetic link in some horses to gain and retain weight easier than others. These horses are often referred to as “easy keepers.”

Insulin is the hormone that allows the body’s cells to take in sugars from the blood. Genetically, some of us are predisposed to secrete more insulin than others when eating a meal (especially one made up of carbohydrates). Additionally, all of the cells that bind insulin (muscle and fat – for the purposes of this post) may also have reduced sensitivity to its effects. This creates a vicious cycle where the body is releasing more and more insulin (hyperinsulinemia – elevated levels of insulin in blood); which reduces the breakdown of FAT stores from the body (insulin inhibits lipolysis).

Does this mean that your horse is destined to be overweight eventually developing laminitis? Not necessarily.

Diagnosing whether your horse actually has EMS and insulin dysregulation if fairly simple. In a recently published article by Dr. Nicholas Frank, DVM, PhD, the diagnostic testing and criteria are outlined. The fasting Oral Sugar Test (OST – we love acronyms in medicine!) is the preferred method for stimulating insulin release because it allows practitioners to compare a horse’s insulin release with a known amount of sugar with the “normal” amount of insulin that SHOULD be released when the average horse is given the same quantity of sugar. The OST consists of giving 75 ml of Karo syrup orally per 1000 pounds body weight , collecting serum samples at 60 and 90 minutes and in some breeds such as Crillio at 120 minutes to assay Insulin concentrations.

Treatment options depend on the severity of the insulin dysregulation; which is why it’s important to perform OST before starting any kind of therapy. Cornell’s Animal Health Diagnostic Center has a nice synopsis of all of the currently recommended diagnostic tests for EMS; it can be found HERE.  To summarize:

  1. Assess insulin levels
  2. Oral Sugar Test
  3. Assess leptin levels (Which quantitates the extent of obesity)
  4. Assess Thyroid levels (T3, T4 & Free T4)

Dietary Management of EMS

The overall goal in EMS is to reduce the insulin levels in the body which can be achieved by reducing the amount of simple sugars in the diet. If any sweet feeds are being used, discontinue and replace with hay. There are numerous hypoglycemic concentrate rations are available on the market. Supplement any other energy requirements with some form of vegetable oil (1-2 cups/day). A grazing muzzle may also be necessary to limit the amount of grass and the associated fructans ,which are elevated by seasonal climatic changes, consumed.

Exercise is also warranted for treatment as it can reduce obesity and improve insulin sensitivity which results in a lowering of serum Insulin concentrations in as little as 4 days.  Moderate exercise  such as hand walking or swimming is highly recommended. 

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In severe cases of insulin dysregulation, a major concern is developing laminits; this is where medication therapy is indicated. Levothyroxine is a thyroid hormone that affects metabolism. A commercially available product by Lloyd is readily available in powder form. The starting dose is 0.1 mg/kilogram but it can also be administered at fairly high doses (48 mg of Levothyroxine Sodium – or 4 scoops) to quickly increase metabolic rate and fat stores.

Compounded flavored oral and MP injectable (once per month injection)  thyroxine can also be prescribed to reduce obesity. It usually takes 3 to 4 months of appropriate thyroxine therapy to achieve significant loss of body fat resulting in lowering of serum insulin. Several research studies have clearly shown that prolonged elevation of serum Insulin can cause laminitis. The target level of fasting serum insulin levels is 20 uU/ml .

Alternatively, a once a month Levothyroxine injection developed here at BET Pharm is available. It comes in a single dose vial and is injected just once every 30 days rather than daily oral administration. This has obvious benefits over a daily therapy but most of all lowers the chance for non-compliance. With an oral product, is the horse receiving the entire dose or is it falling to the bottom of the feed and being swept away? With a single dose given just once a month you can be sure that the horse is getting the entire dose and it is much less work.

Metformin has also been shown to improve insulin utilization however it’s poorly absorbed and can cause oral irritation (recommend rinsing mouth post administration to reduce irritation and prevent ulcers).


Next week we’ll be taking a closer look at PPID. We’ll discuss the signs and symptoms as well as diagnostic criteria and treatments.

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