Carbohydrates are the primary energy source in your horse's diet, but the type of carbohydrate matters enormously. Structural carbohydrates (fiber from hay and pasture) are fermented slowly in the hindgut and are the safest, most natural energy source for horses — this is covered under the Fiber guide. Non-structural carbohydrates (NSC), which include starches and simple sugars from grains, concentrates, and lush pasture, are digested in the small intestine and provide quick-release energy. The critical concern is that horses have a limited capacity to digest starch in the small intestine. When starch intake exceeds roughly 2 grams per kilogram of body weight per meal, undigested starch spills into the hindgut, where it is rapidly fermented by lactic acid-producing bacteria. This crashes the hindgut pH, kills beneficial fiber-fermenting microbes, releases endotoxins into the bloodstream, and can trigger laminitis — a devastating, potentially career-ending or life-threatening inflammation of the hoof laminae.
For a 500kg horse, keep total non-structural carbohydrate (NSC) intake below 1 kilogram per meal and ideally below 2 kilograms per day — that is roughly the starch content of 2 to 3 kilograms of oats. For horses prone to laminitis, metabolic syndrome, or Cushing's disease, NSC should be restricted to less than 10 to 12 percent of total diet, which may mean soaking hay to leach out sugars and avoiding grain entirely. Think of NSC in your horse's diet the way you think of sugar in a diabetic's diet: some is fine, but the dose makes the poison.
37.25% of daily nutrient intake
Carbohydrates makes up 37.25% of your horse's total daily nutritional requirements by weight.
Horses do not require non-structural carbohydrates at all — they can meet all energy needs from fiber fermentation and fat. There is no carbohydrate deficiency syndrome in horses. A horse with insufficient total energy will lose weight, but the solution is more forage or fat, not more starch.
This is where carbohydrates become dangerous for horses. Excess starch and sugar cause hindgut acidosis (disrupted microbial balance, diarrhea, gas colic), laminitis or founder (inflammation and potential rotation of the coffin bone inside the hoof — the most feared complication), obesity, insulin resistance, equine metabolic syndrome, Cushing's-related laminitis flares, and excitable or “hot” behavior from blood sugar spikes. Laminitis from carbohydrate overload can be triggered in a single meal and can permanently disable a horse.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 0 | 2000 | g | Non-structural carbohydrate (starch + sugar) maximum for a 500kg horse. Keep below 2kg total NSC per day, and below 1kg per meal to avoid hindgut starch overload. Metabolically compromised horses should receive far less. |
| Working / Active | — | 0 | 3000 | g | Working horses can tolerate moderately more starch for glycogen replenishment, but should still receive it in small, frequent meals rather than one large grain feed. |
Source: NRC 2007, general veterinary consensus
