What to Feed a Horse with EMS

What EMS Means for Feeding

EMS (Equine Metabolic Syndrome) is a condition where the horse's cells become resistant to insulin. When a healthy horse eats sugar or starch, the pancreas releases insulin and cells respond — blood sugar is cleared efficiently. In an EMS horse, cells don't respond normally. The pancreas keeps releasing more insulin, blood insulin levels stay chronically elevated, and that excess insulin directly damages the laminae — the sensitive tissue bonding the hoof wall to the coffin bone. This is why EMS horses are prone to laminitis.

The critical implication for feeding: everything that drives up blood sugar and insulin must be minimized. That means starch (from grains) and sugar (from molasses, lush grass, sweet feeds) are the primary dietary dangers. Fiber-based energy — from beet pulp, soybean hulls, alfalfa — produces a much smaller insulin response because it is fermented in the hindgut rather than absorbed as glucose in the small intestine.

The NSC Limit and Why It Matters

NSC (Non-Structural Carbohydrates) is the sum of starch and sugar in a feed. It is the most important number on any label for an EMS horse. The widely cited target is total diet NSC below 10% — this applies to the combined diet including hay, not just the bagged feed.

For horses with active laminitis or severe insulin dysregulation, the target tightens to below 7% NSC.

Why does the 10% number matter? Research by Dr. Nicholas Frank, Dr. Kathleen Gustafson, and others has shown that horses with insulin dysregulation have an exaggerated insulin response to dietary NSC even at levels healthy horses tolerate easily. The goal is not to eliminate carbohydrates — fiber is a carbohydrate and essential for hindgut health — but to minimize the fast-digesting, blood-sugar-spiking fractions: starch and simple sugar.

Feeds That Work for EMS Horses

The following feeds from our verified library have NSC values compatible with EMS management. All values are from manufacturer data or verified retailer sources:

Feeds to Avoid

These feed types are not appropriate for horses with EMS:

Hay Management for EMS Horses

Hay typically makes up 80–90% of an EMS horse's diet by weight, so hay NSC matters as much as feed NSC — often more. The combined diet NSC is what the horse's insulin system actually sees.

Get your hay tested

Hay NSC varies dramatically — from below 6% for mature grass hay to above 20% for lush first-cutting orchard grass or certain regional hays. You cannot guess by looking at it. Equi-Analytical Laboratories (equi-analytical.com) is the standard reference lab for horse hay testing. Order the "Trainer" or "Core" package and request ESC (ethanol-soluble carbohydrates) and starch separately.

Hay selection guidelines

• Target hay NSC below 10% (ESC + starch combined) for EMS horses
• Mature grass hay — timothy, orchard grass, brome cut at late maturity — tends to be lower in sugar than early-cut hay
• Alfalfa hay has naturally low NSC (typically 8–12%) but high protein and calcium — appropriate for EMS horses in moderate amounts if Ca:P ratio is managed
• Avoid spring/early summer cuttings of grass hay — highest sugar content due to rapid growth
• Avoid hay cut in the afternoon when plant sugar content peaks from daytime photosynthesis

Soaking hay

Soaking hay in cold water for 30–60 minutes leaches water-soluble sugars (WSC/ESC), reducing NSC by approximately 30% on average — though results vary widely. Soaking does not reduce starch. It does reduce potassium (important for horses on diuretics) and some vitamins. Drain and dispose of the soak water. Feed soaked hay immediately — don't leave it sitting.

Soaking is a useful tool when hay testing shows borderline NSC or when tested hay is unavailable, but it should not substitute for testing. Soaking an unknown hay that might be 20% NSC still leaves you with an unknown NSC — just lower than before.

Pasture and Grazing Rules

Pasture grass is the highest-risk food source for EMS horses. Lush, actively growing grass can reach 25–35% NSC in spring and early fall — far exceeding the 10% target for the entire diet. Many horses develop their first laminitis episode from unrestricted spring pasture access.

High-risk periods

• Spring flush — grass grows rapidly, stores high sugar. The highest-risk period of the year.
• Fall regrowth — after summer dormancy, grass accumulates sugar again
• Sunny afternoons — grass sugar peaks during daytime photosynthesis
• After frost — stressed grass concentrates sugar as a freeze-protection mechanism. Never turn EMS horses onto frost-affected pasture.
• Drought stress — stressed grass also accumulates sugar

Safer grazing approaches

• Graze in early morning (before 10am) when overnight respiration has consumed some accumulated sugar
• Use a grazing muzzle to reduce intake by 75–80%
• Limit to a dry lot with tested hay during high-risk periods
• Strip grazing mature, stemmy pasture that has been allowed to grow tall and seed out

How to Transition an EMS Horse Safely

Changing the diet of any horse too rapidly disrupts the hindgut microbial population and can cause digestive upset, loose manure, or colic. EMS horses are no different. Transition over 7–14 days minimum.

Transition protocol

1. Days 1–3: 75% old feed / 25% new feed
2. Days 4–6: 50% old feed / 50% new feed
3. Days 7–10: 25% old feed / 75% new feed
4. Day 11+: 100% new feed

During the transition, also begin reducing pasture access gradually if the horse was previously on turnout. Remove grain supplements one at a time rather than all at once.

If Your Horse Also Has PPID (Cushing's Disease)

PPID (Pituitary Pars Intermedia Dysfunction, commonly called Cushing's disease) is a separate condition from EMS but causes very similar insulin dysregulation through a different mechanism — overproduction of ACTH and cortisol from a dysfunctional pituitary gland. Many older horses have both conditions simultaneously.

The dietary management is identical to EMS: total diet NSC below 10%, no grain, no molasses, low-NSC hay. PPID horses also lose muscle mass more readily, so protein quality matters — ensure adequate lysine from soybean meal-based feeds or targeted supplementation. Vitamin E (natural d-alpha-tocopherol) at 1,000–2,000 IU/day supports immune and muscle health in PPID horses.

PPID is also treated medically with pergolide (Prascend) — dietary management alone does not address the underlying hormonal dysfunction. Diet controls insulin; medication controls ACTH.

Supplements Worth Considering

These supplements have research support for EMS horses specifically. Always check that supplements don't contain sugar-based carriers:

• Magnesium — some research suggests magnesium improves insulin sensitivity. Common in EMS-targeted products. Magnesium oxide is the typical form. 3–5 grams/day for a 1,100 lb horse.
• Chromium — potentiates insulin action at the cellular level. FDA-approved in horse feeds as chromium propionate. Emerging evidence, not definitive.
• Natural Vitamin E (d-alpha-tocopherol) — antioxidant support, especially for horses without pasture. 1,000–2,000 IU/day minimum. Use natural form — significantly more bioavailable than synthetic.
• Spirulina — some evidence for anti-inflammatory effects and improved insulin sensitivity in horses. Limited horse-specific research but low risk.
• Hindgut buffer / yeast culture — supports stable hindgut environment during dietary transition. Low-NSC formulations available.

Do not stack multiple supplements without checking each for hidden sugar or starch carriers. Many "calming" supplements and hoof supplements use molasses as a palatability aid — check every ingredient list.