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Equine Metabolic Syndrome (EMS)

EMS is an endocrine disorder characterized by insulin resistance, increased blood insulin level and increased body condition.

Clinical Signs of EMS
• Predisposition to chronic laminitis (founder). Founder episodes occur more frequently around May and June when pasture forage consumption is increased (pasture associated laminitis), but horses with EMS can develop laminitis at any time during the year.

• Maldistribution of fat (cresty neck, fatty sheath, fat around the tail head). Many of these horses are called “easy-keepers”, gaining weight when simply looking at grain! However, some horses with a normal appearance and body condition score are also affected by this syndrome.

• Breeds predisposed to EMS include ponies, Morgan, Arabians, Warmblood breeds and Quarter Horses.

• Equine Cushing’s disease and EMS can share similar clinical findings. However, EMS can be observed as young as 3 years and Equine Cushing is a disorder of older horses.

The physical appearance of a horse can be suggestive of EMS (overweight, fat deposits behind the shoulder, in the crest of the neck and at the tail head). Body condition score helps identifying over-weight horses. A horse that is obese (body condition score of 7 or greater), is more likely to develop EMS.
Body Condition Score Description
7: Crease down spine; ribs have fat filling between them; tail head spongy; fat deposits along withers and neck and behind shoulders
8: Apparent crease down spine; ribs difficult to feel; soft fat surrounding tail head; fat deposits along withers, behind shoulders, and on inner thighs; neck is large
9: Obvious crease down spine; patchy fat on ribs; bulging fat on tail head, withers, behind shoulders, and on neck; fat fills in flank and on inner thighs

Testing for EMS
In the past a baseline insulin alone was used to test for EMS, however some horses with EMS will have a normal baseline fasted insulin and only test positive using the oral sugar test. In an attempt to avoid making a false negative diagnosis, and to insure that all horses with EMS are managed correctly, the oral sugar test has become the test of choice for the diagnosis of EMS.

The oral sugar test is the most sensitive way to diagnose EMS. The oral sugar test requires the owner administer 0.07ml/pound light Karo Syrup using an oral dosing syringe (70ml for a 1000 pound horse). The vet comes to draw blood for insulin testing 60-90 minutes after the Karo Syrup was given.  Horses that have insulin values greater than 60 uU/mL at 60 to 90 minutes are diagnosed with EMS.

Medication must be combined with management strategies (including diet and exercise) to control EMS.  Levothyroxine (Thyro-L) is a medication given to improve weight loss and insulin sensitivity. Metformin is another medication that increases the activity of insulin. Your veterinarian can determine if your horse needs medication to control its metabolic status.

Management Strategies

Horses with EMS should be fed a diet low in sugars or non-structural carbohydrates (NSCs). Pasture is often restricted due to its high NSC content. Grazing muzzles can be used to limit grass consumption.

The diet should be based on a mature grass hay (1st cut hay) fed at 1.5% body weight. For example, a horse weighing 1000 pounds would receive 15 pounds of hay per day. Weigh your hay on a scale to insure appropriate feeding . Since 15 pounds of hay may only equal 3-4 flakes, a slow-feeder hay bag can be used to help your horse savor every blade and keep your horse busy eating throughout the day.

We recommend that your hay be analyzed for NSC content and the diet adjusted accordingly.

Because a forage-only diet often doesn’t provide adequate protein, minerals and vitamins, you may consider adding supplements in your horse diet, such as Vitamin E (1000 units per days) and selenium (1 mg per day).

Make sure to introduce dietary changes gradually and to avoid prolonged periods of feed with-holding. Abrupt starvation in obese horses, ponies and donkeys can cause serious illness due to hyperlipemia.

Exercise Physical activity helps to achieve weight loss and improves insulin sensitivity. Thus, it is suggested to introduce exercise 2-3 sessions per week for 20-30 minutes/session and to increase progressively the intensity and duration.

EMS can be a life-threatening disease when horses are affected by chronic laminitis. Laminitis can cause significant pain leading to humane euthanasia. Identifying EMS early and instituting management changes can reduce the occurrence of this serious complication.