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EQUINE METABOLIC SYNDROME: CAUSES, SIGNS, TREATMENT AND PREVENTION
Adapted from the My Horse University Horse Nutrition online course

Causes and Signs
Equine Metabolic Syndrome (EMS) is also called Peripheral Cushing's Disease or insulin resistance. EMS has some similar signs to Equine Cushings Disease, but it is a different disease with different underlying causes. Clinicians, however, believe that Equine Metabolic Syndrome could be a factor in horses that develop Equine Cushing's Disease in their later years. Horses with EMS will be insulin-resistant, will be prone to or have laminitis, and will show abnormal fat deposits.

EMS is caused when fat cells or adipose tissue produce high levels of adipokines, a protein hormone that leads to an increase in cortisol. As a result of the abnormal hormone production, a horse’s normal response to the hormone insulin is disrupted, resulting in high insulin and glucose blood concentrations. The horse cannot properly metabolize carbohydrates, including starches and sugars. This mechanism can trigger the onset of laminitis.

Certain management practices such as feeding high caloric diets to relatively inactive horses can predispose a horse to EMS. Equine Metabolic Syndrome can occur at any point after a horse reaches maturity.  Management practices that predispose a horse to EMS are most likely initiated during the first 10 years of a horse's life. Some breeds such as Miniature horses and donkeys, ponies, Paso Finos, and Morgans tend to be more predisposed to this syndrome.

Equine Metabolic Syndrome is usually first recognized when chronic recurrent laminitis is seen in fat horses that lack other laminitis triggers. The most common clinical signs are abnormal intra-abdominal fat deposits (belly fat) as well as fat accumulation in the crest of the neck, over the rump and in the sheath of male horses. These horses will usually have a high body condition score of 7 (Fleshy) or higher. However, other equine may just have abnormal fat deposits. There is currently no single diagnostic test that can definitively diagnose EMS, but elevated levels of glucose and insulin after fasting along with negative results from the dexamethasone suppression test (DST) used to diagnose Equine Cushing's are good indicators of EMS. Despite the similarity in symptoms, it is important to distinguish between the two diseases so that the appropriate treatment can be started.


The donkey in this photo has abnormal fat deposits over the rump.

Treatment and Prevention
Insulin sensitivity and glucose tolerance can be improved by dietary restriction and exercise aimed at reversing obesity. Here are some strategies that can be used in the treatment of this disease.

  • Reduce calorie intake and eliminate simple sugars (carbohydrates).
  • Feed moderate quality grass hay at 1½ % of ideal weight. You can test the hay for the amount of simple carbohydrates, if the horse is severely affected or not responding to diet well.
  • If the horse can tolerate pasture, use a grazing muzzle and allow the horse to graze in the mornings before the sugar content rises with sun exposure.
  • Other acceptable feeds are grass hay cubes and beet pulp without molasses.
  • DO NOT feed grains, carrots, apples or sweet feeds.
  • STOP supplements that are soybean meal-based or high in sugar content.
  • If greater dietary energy is needed once obesity has been brought under control and an exercise program has been initiated, grass hay should be supplemented with soaked beet pulp and/or vegetable oil or rice bran rather than grain.
  • Increase exercise, if laminitis is not present or is improving to a degree to allow some exercise.
  • Chromium supplementation is recommended as well as magnesium supplementation to achieve dietary calcium: magnesium ratio of 2:1.

Some research has shown that soaking grass hays in warm water for an hour and half before feeding can reduce the non-structural carbohydrate concentration of the hay by as much as 40%. Even if the hay is soaked for a shorter amount of time or in cold water, there is still some reduction of non-structural carbohydrates because they are water soluble. Soaked hay should be fed immediately to prevent mold formation. Soaking hay is a good practice to use for horses that have metabolic conditions because fresh grass alone can average about 18.7% in non-structural carbohydrates (Feed Composition Library, from Dairy One Forage Laboratory, Ithaca, NY). Feeding warm season grasses like Bermuda grass versus cool season grasses can also reduce the amount of sugars available in the hay.

There are some newer commercial feeds that are formulated for a horse with EMS. They are typically lower in starch and sugars, higher in fiber, and supplemented with vitamins and minerals. They may also have additional fat for horses that need more calories in their diets. There are also some new drugs in various stages of research, but it will probably be years before any are approved as useful and safe in horses.

Lifestyle changes such as increased exercise and improved diet are still the best way to treat this disease.


Do not feed a horse with equine metabolic syndrome apples and carrots

Additional Resources

eXtension News: Not All Horses Should Graze. http://www.extension.org/pages/Not_All_Horses_Should_Graze

University of Minnesota Extension: Equine Metabolic Syndrome (EMS). http://www.extension.umn.edu/horse/components/ems.htm