Equine Metabolic Syndrome (EMS) Explained
EMS is a metabolic disorder of horses built on insulin dysregulation and regional fat. Learn the signs, how it differs from PPID, and why it drives laminitis.
Quick definition: Equine metabolic syndrome (EMS) is a metabolic disorder defined by insulin dysregulation, a tendency to store fat in regional pockets such as a cresty neck, and a high risk of laminitis. Unlike PPID, EMS is driven by genetics, diet, and body fat rather than the pituitary gland, and it can affect horses of any age. It is managed with weight loss, a low-sugar low-starch diet, and exercise.
Equine metabolic syndrome is one of the most important diagnoses for any easy-keeping horse or pony, and it matters even more in seniors because the laminitis it causes can be career-ending or worse. The good news is that EMS is largely a management disease, meaning diet and exercise are powerful tools.
At its heart, EMS is about insulin. When a horse's body handles sugar and starch poorly, blood insulin stays too high, and high insulin is the spark that ignites laminitis. Understanding that single chain of cause and effect explains almost everything about how EMS is managed.
Helpful Products for EMS Horses
Heiro HEIRO Healthy Equine Insulin Rescue
$58.95 on Amazon
Herbal blend with magnesium and vitamin E to support normal metabolic function in insulin-resistant horses.
Equine Veterinary Essentials MetaboBalance Equine Metabolic Support
$54.99 on Amazon
Daily powder formulated to help manage insulin resistance and laminitis risk alongside vet care.
Tough 1 Tough 1 Horse Weight and Height Tape
$5.30 on Amazon
An inexpensive weight tape to track an EMS horse's body weight during a controlled weight-loss plan.
The Three Pillars of EMS
Veterinarians describe EMS as having three connected features. A horse does not need all three to be diagnosed, but they tend to travel together.
- Insulin dysregulation. High resting insulin, an exaggerated insulin response to sugar and starch, or insulin resistance in the tissues. This is the core abnormality.
- Regional adiposity. Fat stored in pockets, most visibly a firm, cresty neck, plus pads behind the shoulders and around the tailhead.
- Laminitis risk. A history of laminitis, or subclinical changes in the hoof seen on x-ray, driven by the high insulin.
Why EMS Matters in Senior Horses
A senior horse can develop both EMS and PPID, and the combination compounds the laminitis danger. Because aging horses are often less active and may be fed generously, an easy keeper can drift into an overweight, high-insulin state without obvious warning until laminitis strikes. Catching EMS before that first founder is the whole goal.
Assessing body condition is central. Use the Henneke body condition score to judge overall fat, but also feel the neck and tailhead specifically, since a horse can carry dangerous regional fat at a fairly average overall score.
How EMS Is Diagnosed
Diagnosis combines the physical picture with blood tests of insulin status. A resting insulin can be a starting point, but a dynamic test such as the oral sugar test is more reliable because it challenges the horse with a measured sugar dose and reveals how high insulin climbs. Your vet will usually also test ACTH to check for concurrent PPID.
Managing EMS Day to Day
Management rests on diet and movement. The core steps are:
| Goal | Practical Step |
|---|---|
| Lower dietary sugar and starch | Feed forage and feeds under about 10 to 12 percent NSC; soak hay if needed |
| Reduce body fat | Controlled calorie restriction; track weight with a tape |
| Limit pasture sugar | Restrict grazing, use a grazing muzzle, avoid lush or frosty grass |
| Improve insulin sensitivity | Regular exercise once the horse is sound |
Keeping the ration low in non-structural carbohydrates is the single most important dietary lever. For help building that ration, see how much to feed a senior horse and our best senior horse feed guide, and read the full clinical picture in equine metabolic syndrome (EMS).
This page is educational and does not replace your veterinarian. EMS is diagnosed with blood tests and managed under veterinary guidance tailored to your individual horse.
Senior Horse Care Planner
Track your senior horse's vital signs, feed and body condition, farrier and dental schedule, medications, and quality of life, all in one printable planner.
Frequently Asked Questions
What is equine metabolic syndrome in simple terms?
Equine metabolic syndrome, or EMS, is a collection of risk factors centered on insulin dysregulation, the horse equivalent of a diabetes-like blood sugar problem. EMS horses tend to gain fat easily, store it in pockets along the crest and tailhead, and have a high risk of laminitis. It is not a single disease but a metabolic state that makes a horse prone to founder.
How is EMS different from PPID?
EMS is driven by genetics, diet, and body fat, and it can affect horses of any age, including younger ones. PPID is a hormonal disease of the pituitary gland that develops with age, usually past 15. The two overlap because both can cause insulin dysregulation and laminitis, and a senior horse can have both at once, which is why vets often test for each.
What is insulin dysregulation?
Insulin dysregulation is the core problem in EMS. It includes high resting insulin, an exaggerated insulin spike after eating sugar or starch, and tissues that respond poorly to insulin. The result is persistently high blood insulin, which is the direct trigger for endocrine laminitis. Vets measure it with resting insulin or, more reliably, an oral sugar test that challenges the horse with a known sugar dose.
What does regional adiposity look like?
Regional adiposity means fat collects in specific pockets rather than spreading evenly. The classic sign is a hard, cresty neck. Owners also see fat pads behind the shoulders, along the ribs, around the tailhead and sheath or mammary area. A horse can show regional adiposity even at a moderate overall body condition score, so check these spots specifically rather than relying on weight alone.
How is EMS managed?
EMS is managed mostly through diet and exercise, since there is no cure. The plan is weight loss for overweight horses, a low-sugar low-starch diet under about 10 to 12 percent NSC, soaked hay if needed, restricted or muzzled grazing, and regular exercise once the horse is sound. In some cases vets add medication to support insulin. The goal is to keep insulin low and prevent laminitis.
Can EMS be reversed?
The underlying tendency does not disappear, but the dangerous part, high insulin and laminitis risk, can improve dramatically with management. Many overweight EMS horses that lose fat and move to a controlled diet see their insulin return toward normal. It takes consistency over months, and the diet and exercise plan usually has to continue for life to keep the syndrome under control.
Are some breeds more prone to EMS?
Yes. So-called easy keepers are at higher risk, including many pony breeds, Morgans, Arabians, Andalusians, mustangs, and gaited breeds. These horses evolved to thrive on sparse forage and store calories efficiently, which works against them on modern rich pasture and feed. Breed is only one factor, though, since diet, exercise, and body fat all shape whether EMS develops.
Need more help with your senior horse?
Browse our guides by topic to find practical solutions.
Wellness Planner: $39