Feeding the Insulin-Resistant (EMS) Horse: A Complete Guide

Insulin resistance and equine metabolic syndrome (EMS) are among the most common reasons owners start reading feed tags. The good news: diet and management make a real difference. This guide covers what EMS is, how feeding fits in, and the questions to bring to your veterinarian.

What is equine metabolic syndrome (EMS)?

Equine metabolic syndrome (EMS) describes horses and ponies with insulin dysregulation (ID), often along with obesity or regional fat deposits, and a higher risk of laminitis. Insulin dysregulation means the body releases too much insulin in response to sugar and starch, or doesn't respond to insulin normally (insulin resistance).

High insulin is closely linked to endocrinopathic laminitis, which is the most common form of laminitis seen by vets. That's why managing insulin is the main goal.

Common signs owners notice

• A cresty neck (a firm, thick crest along the top of the neck)
• Fat pads near the tailhead, over the shoulder or above the eyes
• Easy weight gain, or trouble losing weight
• Previous bouts of laminitis or "sore feet," especially in spring or fall
• Divergent growth rings on the hooves

Not every EMS horse is overweight, and not every overweight horse has EMS. Only testing tells you.

Who's at risk

EMS is more common in ponies, miniature horses, donkeys and certain breeds often described as "easy keepers," such as Morgans, Arabians, Paso Finos, Mustangs and many warmbloods, though any horse can be affected.

How EMS is diagnosed

Your vet will usually combine a physical exam, body condition scoring and blood tests. A common test is the oral sugar test, in which the horse receives a measured dose of corn syrup and insulin is checked afterward. Resting insulin and other tests may also be used. Because PPID (Cushing's disease) often occurs alongside EMS in older horses, your vet may test for that too.

Follow-up testing helps show whether the diet and management plan is working.

The four pillars of managing EMS

Veterinary guidelines generally focus on four areas. Your vet will tailor them to your horse.

1. A low-sugar, low-starch diet

The goal is to limit the sugar and starch that drive insulin spikes. Many guidelines suggest keeping the whole diet under about 10% NSC (measured as ESC + starch) for high-risk horses. In practice that usually means:

• Tested, low-sugar hay as the foundation (see our hay testing guide)
• No grain, sweet feed or sugary treats
• A ration balancer or vitamin/mineral supplement to cover nutrients hay doesn't supply
• If extra calories are needed, low-NSC sources such as plain beet pulp, soy hulls or modest fat, as your vet advises

2. Weight loss, if needed

Many EMS horses carry extra weight, and weight loss can improve insulin sensitivity. Your vet will set a target and a safe pace. Some guidelines suggest feeding hay at around 1.5% of current body weight per day as a starting point for weight loss, and generally not going below about 1.25% without close veterinary supervision, because severe restriction carries its own risks. Weighing hay is essential; see our body condition score guide to track progress.

3. Controlled grazing

Pasture is often the biggest uncontrolled source of sugar. Grass sugar rises with sunshine and growth, and can be especially high in spring, fall and after frost. Options your vet may discuss include:

• No grazing during high-risk periods, or for horses with active laminitis
• Grazing muzzles, which can substantially reduce intake
• Limited turnout on a dry lot or track system with hay
• Grazing early in the morning, when sugar is usually lowest

4. Exercise, when safe

Regular exercise can improve insulin sensitivity and help with weight loss. But horses with active or recent laminitis may not be able to exercise safely. Always ask your vet before starting.

Choosing feeds and hay for an EMS horse

Here's how the pieces typically fit together for a horse at maintenance:

Soaking hay is sometimes used to reduce sugar, but results vary widely. Ask your vet whether it suits your horse and how long to soak.

Supplements for EMS: what the evidence says

Many supplements are marketed for metabolic horses, including magnesium, chromium, resveratrol and various herbs. Research in horses is limited and results are mixed. They don't replace diet, weight management and exercise. If you're considering one, ask your vet whether it's likely to help your horse, and how it fits with any medication. The Equine Feed Guide flags supplements whose main ingredients have limited research.

Your vet may also discuss prescription medications for some horses. These are decisions for your veterinarian.

Questions to ask your vet

1. What sugar + starch target should the whole diet stay under?
2. Should I test my hay? Should I soak it, and for how long?
3. Is grazing safe right now? How many hours, and with a muzzle?
4. Does my horse need to lose weight? What's the target and a safe pace?
5. How much hay should I feed per day, by weight?
6. Would a ration balancer or vitamin/mineral supplement be right?
7. Is exercise safe, and how much?
8. Should we also test for PPID?
9. When should we re-test insulin?

Enter your horse in the Equine Feed Guide, tick "Insulin resistance / EMS," and use Take to my vet to bring a summary of the current diet to your appointment.

Frequently asked questions

Sources and further reading

• Equine Endocrinology Group (EEG). Recommendations for the diagnosis and management of equine metabolic syndrome.
• American Association of Equine Practitioners (AAEP): owner resources on EMS and laminitis.
• American College of Veterinary Internal Medicine (ACVIM). Consensus statement on equine metabolic syndrome.
• National Research Council. Nutrient Requirements of Horses, 6th revised edition (2007).