Horse Energy & Ration Calculator (NRC Digestible Energy by Workload, Hay vs Grain Split, Weight Change)
Calculate a horse's daily digestible-energy requirement from body weight, workload, growth, pregnancy or lactation using NRC guidelines, then build a ration: how much of your hay meets it, whether grain or a fat supplement is needed, forage minimum checks, and how a calorie surplus or deficit changes weight.
How it works
maintenance DE (Mcal/day) = 0.0303 / 0.0333 / 0.0363 × BW (kg) for easy / average / hard keepers (NRC 2007) · × workload: light 1.2, moderate 1.4, heavy 1.6, very heavy 1.9, late pregnancy 1.2, lactation ≈ 1.7, growing 12–18 mo ≈ 1.45 · ± 2.5 Mcal/day ≈ ± 1 lb/day body weight · hay lb = Mcal ÷ hay DE (capped at max % BW); concentrate lb = remaining Mcal ÷ concentrate DE; forage ≥ 1.5% BW
The National Research Council expresses a horse's needs in digestible energy: a maintenance figure proportional to body weight, scaled up for work, pregnancy, lactation or growth. Hay carries a known number of megacalories per pound, so the requirement translates directly into pounds of hay — and only when the horse cannot eat enough hay (or will not) does grain, or the denser and safer option of oil, fill the gap. The calculator does that arithmetic, keeps forage above the gut-health minimum, and shows how a modest daily surplus or deficit becomes weight on the tape.
Worked example
An average 1,100 lb horse (499 kg) needs 16.6 Mcal at maintenance and about 19.9 in light work. Grass hay at 0.85 Mcal/lb meets that with 23.5 lb a day (2.1% of body weight) — no grain needed. In moderate work (23.3 Mcal) the hay cap of 2.2% BW (24.2 lb, 20.6 Mcal) leaves a 2.7 Mcal gap: about 1.9 lb of a 1.4 Mcal/lb feed, or 1.4 cups of oil. To gain a pound a day the same horse would need about 2.5 Mcal more.
Frequently asked questions
How many calories does a horse need a day?
About 15–17 Mcal of digestible energy for an idle 1,000–1,100 lb horse, 18–20 in light work, 22–24 in moderate work and 26–32 for hard work or a lactating mare. Easy keepers need ~10% less, hard keepers ~10% more. A megacalorie is 1,000 kcal — a 1,100 lb horse at maintenance eats about 16,000 "calories".
Does my horse need grain?
Most horses in light work do not — good hay at 2% of body weight covers energy, and a ration balancer covers vitamins, minerals and protein quality. Grain is for horses that cannot eat enough forage to meet a high requirement: hard work, lactation, growth, seniors with poor teeth. Oil or high-fat feeds add calories with less risk than starch.
How fast should a thin horse gain weight?
About a pound a day — 45–50 lb (one body-condition score point) in six or seven weeks — from roughly 2.5 Mcal a day above requirement, added gradually. Faster gains risk digestive upset; check teeth, parasites and pain first, because a horse that stays thin on adequate calories has another problem.
Related calculators
Equine figures are planning estimates from common husbandry references (NRC 2007, extension services). Individual horses, forage quality, climate and workload vary — weigh hay, body-condition score regularly and work with your vet, farrier and nutritionist.