What is EMS and IR in horses?

Equine Metabolic Syndrome (EMS) is a condition in horses having to do with 1) insulin malfunction, 2) the presence of fat pads, and 3) a reduced ability to lose weight. These three risk factors make horses and ponies more prone to laminitis.

There are two types of insulin malfunction. One is insulin resistance (IR) and the other is hyperinsulinemia (HI). Insulin resistance is a failure of the body to respond properly to insulin. Hyperinsulinemia means high levels of insulin in the blood. Insulin is a hormone released from the pancreas after a meal, depending on how much sugar was eaten. Insulin helps digested sugar circulating in the blood (glucose) get inside cells so it can be used for energy or stored for later.

The second EMS risk factor is the presence of fat pads also called “regional adiposity.” These pockets of fat are commonly seen in the crest of the neck, at the tailhead and across the rump, behind the shoulder, above the eyes and in the sheath or mammary gland.

Owners of EMS horses commonly report their horses have a reduced ability to lose weight, the third risk factor for laminitis. They describe their horses as gaining weight on air often leading to the nickname “air ferns.” While it is most common for EMS horses to be overweight or obese, they don’t have to be. Veterinarians and nutritionists measure the amount of fat cover on a horse with the Body Condition Scoring (BCS) Scale, which ranges from 1 (extremely thin) to 9 (extremely fat). Overweight horses are in the 6 to 7 range and obese horses are in the 8 to 9 range. Ideal is considered a 5.

What causes EMS and IR in horses?
There is no one, single cause for Equine Metabolic Syndrome. Instead, the combination of genetics and environment (diet and exercise) are what puts a horse or pony at higher risk for laminitis. Certain breeds are known to have the so-called “thrifty gene,” including:

  • Ponies
  • Spanish breeds (e.g. Andalusians)
  • Gaited breeds (e.g. Saddlebreds, Paso Finos)
  • Morgans
  • Minis
  • Warmbloods
  • Possibly donkeys (List courtesy of The Equine Endocrinology Group)

For these at-risk breeds, it doesn’t take much inappropriate feeding and underworking to tip them into Equine Metabolic Syndrome. They’re basically “sitting ducks” when it comes to laminitis. This doesn’t mean other breeds are spared, just that it takes more high sugar/starch grain, pasture, and hay – and more stall time – to trigger the gene.

How do I know if my horse has EMS or IR?
Unfortunately, many horses are not diagnosed with Equine Metabolic Syndrome until they already have laminitis. Early signs and symptoms all owners should be looking for (but especially in the breeds listed above) include:

  • Obesity
  • Gaining weight on very little food
  • Reduced ability to lose weight
  • Fat pads (neck, shoulder, tailhead and rump, above the eyes)
  • Subtle lameness
  • Infertility
  • Sheath or mammary gland swelling

Any horse with these signs should be seen by a veterinarian. During the visit, the vet will perform a physical exam and take a complete history. Depending on the situation, they may perform baseline bloodwork and take x-rays of the feet. They may also test for the separate but related condition Cushing’s Disease or PPID (Pituitary Pars Intermedia Dysfunction). These tests will help your veterinarian assess your horse’s overall health and figure out if there are already signs of laminitis.

There are two “dynamic” tests for EMS. A dynamic test is when the veterinarian gives the horse a substance and then draws blood after a period time to measure the horse’s response to it. One is the Oral Sugar Test (OST) and the other is the Insulin Tolerance Test (ITT). The result of either of these dynamic tests helps the vet diagnose insulin resistance and/or hyperinsulinemia, confirming that the horse has Equine Metabolic Syndrome. If there are concerns about administering the dynamic tests, your veterinarian can draw a blood sample to look at baseline insulin levels. Ideally, owners and vets work together to determine the best method of diagnosing EMS in each individual horse.

Back to blog