Adapted from: Diagnosis and Management of Insulin Resistance and Equine Metabolic Syndrome (EMS) in Horses by Nicholas Frank, DVM, PhD, DACVIM University of Tennessee

DEFINITION - Equine metabolic syndrome (EMS) is a term that describes a series of clinical signs that contribute to the development of laminitis (founder) in horses. Although obese horses have long been recognized to be at greater risk for laminitis, it was not until parallels were drawn between metabolic syndrome in humans and the similar condition in horses, that the reasons for that increased risk were better understood and the term EMS was adopted.  While certain breeds seem to be predisposed to EMS (pony breeds, Morgans, Paso Finos, and Arabians), EMS has been diagnosed in a wide variety of breeds.  In general, “easy keeper” breeds are at higher risk than “hard keeper” breeds such as Thoroughbreds and Standardbreds.

Identifying EMS in affected horses/ponies is important because proper management can aid in the prevention of laminitis.


CLINICAL SIGNS that define EMS: 

Obesity   These horses are often described as easy keepers because they require fewer calories to maintain body weight. Not all obese horse have EMS, however, and not all horses with EMS are obese.

Regional Adiposity (fat deposits)   Fat deposits are sometimes  found close to the tailhead, in the sheath, above the eyes, and occasionally as bumps along the sides of the horse.           

Cresty neck  This is often the most obvious physical feature of horses with EMS

 Hyperinsulinemia (elevated blood insulin level)   This can be easily determined by laboratory testing done by your veterinarian

Prior or current laminitis – Episodes may be triggered by grazing lush grass, or may have no identifiable cause.  Mild bouts of laminitis may go unnoticed by caretakers.



When blood glucose levels rise after a meal, the pancreas releases insulin into the blood. Insulin and glucose then travel in the blood to cells throughout the body.

  • Insulin helps muscle, fat, and liver cells absorb glucose from the bloodstream, lowering blood glucose levels.
  • Insulin stimulates the liver and muscle tissue to store excess glucose. The stored form of glucose is called glycogen.
  • Insulin also lowers blood glucose levels by reducing glucose production in the liver.

In a healthy horse, these functions allow blood glucose and insulin levels to remain in the normal range

In horses with EMS, muscle, fat, and liver cells do not respond properly to insulin and thus cannot easily absorb glucose from the bloodstream. As a result, the body needs higher levels of insulin to help glucose enter cells.  This is referred to as insulin resistance (IR).

 It is currently believed that a high circulating level of insulin in the horse with EMS is the trigger for laminitis.


DIAGNOSIS –  EMS may be suspected based on clinical signs and your veterinarian may perform one or both of the following tests:

Baseline Serum Insulin  – This is a simple blood test that is often used as a screening test to detect moderate to severe insulin resistance.  You must keep your horse off  pasture for 12 hours and feed only hay overnight prior to having your veterinarian draw blood (eating either grass or grain will cause insulin levels to increase).   It is not uncommon to see false negatives with this test.  If your horse tests negative (normal) but EMS is still suspected, a more sensitive test (such as the Oral Sugar Test) should be performed.

Oral Sugar Test-      You must keep your horse off  pasture for 12 hours and feed only hay overnight prior to having your veterinarian draw blood (eating either grass or grain will cause insulin levels to increase).  Blood is drawn for a baseline insulin level.  Then a dose of concentrated sugar solution is administered by mouth; blood is again drawn to measure insulin level 60-90 minutes later.  This helps us evaluate your horses' response to sugar intake.

 Pain and stress associated with acute laminitis can  elevate resting serum insulin concentrations in EMS patients.  It is therefore necessary to reevaluate these patients several weeks later after the pain of laminitis has subsided.




  • Reduce body fat mass in obese horses
  • Avoid feeds that exacerbate IR
  • To improve insulin sensitivity and decrease the threshold for laminitis


Weight loss in obese horses

Obese horses that are easy keepers should be placed on a simple diet of hay and a vitamin/mineral supplement.  Concentrates are not necessary for these horses.

Hay should initially be fed at 1.5%  body weight (15 pounds of hay for the average 1000 pound horse), then reducing this amount to 1.5% of ideal body weight until weight loss is achieved. 

DAILY exercise will help your horse/pony lose that extra weight; it will also increase insulin sensitivity, thus decreasing the risk of laminitis.  Horses and ponies with EMS should be walked on a lead rope, worked on a lunge line, or ridden daily.  If your horse is suffering from laminitis, wait to begin exercise until he is completely recovered.

Avoid feeds that will exacerbate IR - A horse with EMS is similar to a person with diabetes, excess sugar must be avoided.  Treats containing sugar and sweet feeds must be eliminated from the diet....that means no apples, carrots, or cookies.


Hay - It is also important to feed hay with low (<12%) non-structural carbohydrate (NSC) content.  NSC’s include simple sugars, starch, and fructans.  If the NSC of your hay exceeds 12%, soaking it in cold water for 30 minutes prior to feeding will lower the sugar content.  It does not matter if you feed grass or alfalfa hay as long as the NSC has been measured.  It has not been determined whether the protein, vitamin, and mineral content of mid-quality hay is adequate. In order to address these concerns, provide a balanced vitamin and mineral supplement, and sometimes a protein supplement may also be required.

When access to green grass is restricted, so is intake of vitamin E. It is  recommend that horses with EMS receive an additional 1,000 IU vitamin E daily.  Water-dispersible liquid formulations of alpha-tocopherol are about 6 times more bioavailable than synthetic vitamin E.

Water dispersable forms commercially available:
Nano•E, Kentucky Equine Research, Versailles, KY
Elevate WS, Kentucky Performance Products LLC, Versailles, KY
Emcelle, Stewart Products, Bedford TX

Pasture - There is no way to control sugar intake if your horse grazes freely.  Pasture grass is one of the largest sources of sugar in a horse’s diet.  Sugar levels of pasture grass fluctuate with season of the year and the time of day.  Access to pasture must therefore be restricted or eliminated when managing horses and ponies with EMS. Sometimes this is only necessary for weeks or months until the ideal body condition has been achieved, but other severely affected horses must be permanently housed in dirt paddocks because they are extremely sensitive to changes in pasture grass nutrient content. Most horses and ponies with EMS can be managed by limiting grazing time to 1 to 2 hours per day, housing in a grass paddock, strip grazing using an electric fence, or using a grazing muzzle.

 Basic guidelines for lowering the risk of pasture-associated laminitis include avoiding times when the grass is

  1. Turning green and growing quickly (spring)
  2. First drying out at the beginning of a summer drought
  3. Rapidly growing after a heavy summer rain
  4. Entering winter dormancy (fall)

 In addition, the sugar content of pasture grass is highest during the day and lowest at night or very early in the morning.


DRUG THERAPY - Most horses or ponies with EMS can be effectively managed by controlling their diet, instituting an exercise program, and limiting or eliminating access to pasture. However, there are times when these strategies will not improve the situation fast enough to prevent additional episodes of laminitis. In these situations, drug therapy is warranted to lower the likelihood of subsequent laminitis episodes that could cause permanent damage to the feet. Weight loss can be accelerated and insulin sensitivity improved by administering levothyroxine sodium in the feed.

When levothyroxine treatment is discontinued, it should not be stopped abruptly. Horses should be gradually weaned off the drug.


Management of Lean Horses with Regional Adiposity 

Some insulin resistant horses are leaner with respect to overall body condition, but exhibit regional adiposity.  These horses may be older and suffer from equine Cushing’s disease.  Other horses may be exercising strenuously or competing, so they require more calories.  If hay is not sufficient to provide these calories, a concentrate must be selected. 

Thinner insulin resistant horses can usually be safely fed concentrates, but care must be taken to provide calories without exacerbating IR. There are three considerations when evaluating feeds for insulin resistant patients: 1) the carbohydrate composition of the feed, 2) the glycemic response that will follow ingestion, and 3) the feeding practices of the facility. For instance, many sweet feeds have a high starch and sugar content, so the resulting glycemic response is likely to exacerbate IR when these feeds are provided as large meals. Feeds that contain less starch and sugar are more appropriate in these situations and it is advisable to feed smaller amounts more frequently and provide hay before concentrates. We use several strategies when managing leaner insulin resistant horses that require additional calories and the strategy used depends largely upon the appetite of the individual patient. These strategies include:

  1. Feeding a diet consisting of hay with a low (< 12%) NSC content, soaked molasses-free sugar beet pulp, balanced vitamin and mineral supplement, and 0.5 cup (equal to 125 mL; contains approximately 100g fat) rice bran oil or canola oil added to the feed twice daily.

  2. The same diet with a commercial low-starch specialty feed substituted for beet pulp.

  3. Feeding either of the two diets described above, with rice bran substituted for oil. Rice bran contains approximately 20% fat and we usually recommend that 1 lb (approximately 90 g fat) be fed twice daily.

  4. Feeding a pelleted feed designed for geriatric horses to older animals with pituitary pars intermedia dysfunction (PPID).

Horses with finicky appetites sometimes refuse to eat beet pulp or specialty pelleted feeds. If this is the case, clients may have to try several varieties of specialty feed until an acceptable one is found. These horses may also require a transition period as they adapt to the beet pulp or the specialty feed. During this period, we sometimes forced to feed oats with added rice bran or oil (in addition to hay) to horses that refuse lower NSC feeds. This is not an ideal diet for insulin resistant horses because oats contain more hydrolyzable NSC (e.g., starches) than most pelleted feeds, but we attempt to lower the glycemic response by feeding smaller meals more frequently (3 to 4 times daily) and asking clients to feed hay 15 to 30 minutes before concentrates.

Beet pulp is recommended for thinner IR horses because it provides calories, but it is not appropriate for obese horses, except as a treat (0.5 cup after soaking) to aid in the delivery of supplements. Sugar beet pulp is rich in rapidly fermentable carbohydrate, so addition of this ingredient to pelleted feeds lowers the hydrolyzable carbohydrate content. It also expands when soaked in water, so beet pulp provides bulk to satisfy the horse's appetite. Clients should soak the beet pulp prior to feeding because this will lower the risk of esophageal obstruction (choke) and remove molasses if it has been added.


Examples of very low starch and sugar feeds:

  • Alfalfa pellets
  • Other hay pellets
  • Beet pulp, low molasses content - soak in water
  • Complete feeds - meant to replace hay if needed
  • Dengie or chaff products
  • Chopped hay products

Examples of low starch and sugar feeds*:

*In general, feeds higher in protein and fat will be lower in starch and sugar. Ingredients such as soy hulls, beet pulp, bran, wheat brans, and wheat middlings are relatively low in starch and sugar.

Below are examples of low starch and sugar feeds, there are many others. If in doubt, contact the company and ask about starch and sugar content. Look for feeds no more than 33% starch and sugar.

If you can see grains in the product it is likely too high in starch and sugar for an IR horse.

  • Nutrena Safe Choice
  • Senior feeds
  • LMF Stage 1
  • LMF Complete
  • Equi-Pro Carb-Safe
  • Platform horse feeds
  • Triple Crown Senior, Complete, Growth
  • Triple Crown Lite
  • Triple Crown Low Starch
  • Purina WellSolve L/S and W/C 
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