It’s spring! The weather is warming and the trails are calling, but you’ve got the “pudgy pony blues.”

After taking some blood samples, your veterinarian has diagnosed your beloved gelding with Equine Metabolic Syndrome (EMS). You knew something was wrong, because he’d gone from pleasantly plump to downright obese. Plus patches of fat has accumulated at the crest of his neck and the base of his tail. Despite a strict diet and exercise galore, he just can’t seem to shed that fat. And he tires rather easily now, too.

Don’t despair. This condition is more common than you might think. And you and your veterinarian can head off the worst effects of EMS by devising a treatment strategy.

So … what exactly is EMS?

EMS is a disorder characterized by insulin dysregulation, or the inability to metabolize carbohydrates and regulate blood insulin levels correctly. (In the past, the clinical signs of this disorder have been known as hypothyroidism, pre-laminitic syndrome, peripheral Cushing’s disease, or “syndrome X.”)

As you might recall from biology class, insulin isa hormone secreted by the pancreas after a meal. It is released into the bloodstream after carbohydrates are broken down into glucose during digestion, causing the blood glucose (blood sugar) levels to rise.

One of insulin’s primary functions is to enable the transfer of that glucose from the blood into the body’s cells, where it is used to create energy. Once that transfer occurs, the blood glucose levels drop back down, and insulin’s job is done until the next meal.

Unless, that is, something goes wrong in the regulation process. In what is called insulin resistance, the fat deposits in affected horses release hormones that adversely affect the ability of the body’s tissues to respond normally to insulin. This causes a buildup of excess glucose in the blood and prompts the release of more and more insulin, often overwhelming the pancreas.

In humans, this kind of abnormal response can lead to type 2 diabetes. In horses, the result is what we now call Equine Metabolic Syndrome.

1. Breed, environment and other facts affect a horse’s susceptibility to EMS

1. Several genetic, environmental and physiological factors can contribute to EMS. Some breeds or types of horses are inherently prone to this disorder. These include Arabians, Morgans, Paso Finos, Saddlebreds and warmbloods. Donkeys and ponies are also at high risk. However, any “easy keeper” that becomes obese on very little feed can develop EMS. The classic trigger is a diet high in sugar—too much grain or forage high in nonstructural carbohydrates (NSCs). This, combined with a lack of regular exercise, can set the stage for EMS. The condition generally appears between the ages of 5 and 15 years.

As you’ve no doubt guessed, typical signs of EMS include increased appetite, excessive weight that can’t be lost and those characteristic fat deposits (although not every EMS horse is fat). Repeat instances of laminitis and other metabolic issues—occasionally at the same time—are other possible clues that your horse has EMS. So is an unusual amount of fatigue. If your horse is a breeding animal, infertility can be another sign.

2. Prompt diagnosis is important

Early diagnosis of EMS is essential for the best possible outcome. So, if your horse is an “easy keeper” and overweight despite your best efforts to keep him trim—or if he has unusual fatty deposits or a nagging, unexplained lameness in a forelimb—it’s wise to get him professionally evaluated for this disorder.

Your veterinarian may screen for EMS by measuring blood insulin and glucose concentrations from samples taken first thing in the morning, after your horse has been fasted for six to eight hours. This is the best way to diagnose moderate to severe cases of insulin dysregulation.

Dynamic tests

Dynamic tests that assess the body’s responses to a “glucose challenge” may be necessary to diagnose EMS in horses whose metabolic signs are not yet pronounced enough to detect the usual way. In one of these challenges, the Oral Sugar Test (OST), the horse is fasted for three to 12 hours and then given an oral dose of corn syrup. Blood samples are collected prior to and 60 to 90 minutes after corn syrup administration. The blood samples are tested for insulin to determine the horse’s response to a large increase in blood glucose concentration. EMS horses will demonstrate a large spike in blood insulin levels after corn syrup administration, while normal horses will not exhibit a pronounced spike in blood insulin concentration.

An insulin tolerance test (ITT) can also be performed to measure the ability of your horse’s tissues to take up glucose (insulin sensitivity). This involves comparing the glucose concentration of a baseline blood sample to that of a sample taken half an hour after a dose of insulin is administered.

Rule out PPID

Note: When screening an older horse it’s important to rule out an age-related endocrine disorder called Pituitary Pars Intermedia Dysfunction (PPID, or equine Cushing’s disease). Unfortunately, the two can coexist, with PPID believed to worsen insulin dysregulation in horses also affected by EMS.

3. What treatment can do

Treatment of EMS is important, even if your horse is more “pasture ornament” than athlete. Why? Left untreated, this disorder can lead to painful complications. One of the most serious of these is laminitis, which can be crippling and even fatal.

For individuals who are “easy keepers” and obese (as most EMS horses are), simple changes in management can encourage weight loss. This should improve insulin sensitivity and help control the disorder.

But here’s the thing: Merely cutting your horse’s rations may not be enough. It is the restriction of carbohydrates that is critical to decreasing his body’s glycemic and insulinemic responses. Even if your horse consumes only forage, limiting his grazing is especially important in the early spring and autumn, as well as in the afternoon, when pasture grass is richest in natural sugars. (Grazing muzzle to the rescue!)

Hay can be an issue, too; consult your veterinarian about the most appropriate types to feed and consider having each load tested for NSC content. Ration balancers or complete feeds designed for horses with insulin dysregulation may also be useful.

If these dietary tweaks aren’t enough to reduce your horse’s weight, additional exercise may be prescribed.

Finally, if management changes don’t work, your veterinarian might suggest medical therapy with drugs like thyroxine or metformin to help stimulate weight loss and regulate insulin responses. Your veterinarian may also recommend that you add a metabolic supplement to your horse’s regimen.

4. Preventive measures

To help prevent EMS—particularly in those high-risk, “thrifty” breeds—it’s best to feed using an ideal body condition score as your guide rather than just “eyeballing it.”

Keep in mind, too, that horses who are predisposed to this disorder will always need low-carbohydrate hay or pasture grass. That means their hay should ideally be tested for NSC levels. Their access to pasture should also be limited during periods of high sugar content (early spring and autumn), with early morning grazing preferred.

And don’t forget regular exercise! It’s just as important for horses as it is for humans.

So, there you have it – the basics of EMS in four key takeaways. Take a deep breath, hug your horse, and know that you’ve got this!

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