Hay is the foundation of almost every horse's diet, but many owners still feed it by eye, by flakes, or by how full the haynet looks. None of those methods tell you how much forage a horse is actually receiving.
A more reliable approach rests on three numbers: body weight, dry matter and forage quality. Once those three are understood, working out a horse's real hay requirement becomes straightforward.
Start With Body Weight
Veterinary nutrition guidance generally recommends 1.5 to 2% of body weight in forage per day, on a dry matter basis. Many horses will comfortably eat more, and total dry matter intake in healthy horses commonly reaches 2 to 2.5% of body weight. For a 550 kg horse, that works out to roughly 8.25 to 13.75 kg of dry matter a day. Below about 1.25% of body weight, forage should not be restricted further without veterinary supervision, since extreme restriction carries its own metabolic risk.
Those figures describe dry matter, not the weight of hay physically placed in the stable. That distinction changes the maths.
Hay Is Not 100% Dry Matter
Even well-dried hay still holds water. Our current Meadow Hay batch is independently analysed at 88% dry matter, with 8.1% crude protein, 4.5% NSC and 1.86 Mcal of digestible energy per kg of dry matter. So 10 kg of this hay in a stable delivers 8.8 kg of actual dry matter, not 10. For a 500 kg horse, that is close to 1.76% of bodyweight in forage dry matter, a detail that "10 kg of hay" alone never reveals.
Our Own Reference Horse
On our Science of Feeding page we use a 550 kg horse in light work as our working example, and feed it 11 kg of Meadow Hay a day, as fed. At 88% dry matter that is 9.7 kg of forage dry matter, about 1.8% of bodyweight, which calculates out to 784 g of crude protein and 18.0 Mcal of digestible energy: the horse's full protein requirement (770 g) from forage alone, and roughly 82% of its daily energy need (22 Mcal). The calcium to phosphorus ratio from that same hay comes out at 1.9:1, comfortably inside the 1.5 to 2:1 range nutritionists look for.
This is what forage analysis is for. Instead of asking how many kilos a horse eats, you can ask how much of its actual requirement those kilos cover.
Why 10 kg of One Hay Is Not the Same as 10 kg of Another
Two horses can both receive 10 kg of hay a day and still be on very different diets. The American Association of Equine Practitioners uses a simple comparison: hay at 2.2 Mcal per kg of dry matter delivers meaningfully more energy than hay at 1.8 Mcal per kg, at the exact same intake. Over a month, that gap adds up. Weighing hay is step one. Knowing what is actually in it is step two, which is why every Prime Hay batch is lab-tested rather than sold on appearance alone.
Why Forage Should Not Be Cut Too Far
Horses evolved to eat fibrous forage in small amounts, almost continuously. That is not only about calories: chewing hay produces saliva, the horse's main buffer against a stomach that produces acid around the clock. The Merck Veterinary Manual places forage at the centre of the equine diet for exactly this reason, and notes that horses on good forage often need little or no concentrate on top.
Cut forage too far and a horse spends longer periods with an empty gut, which usually means larger, starchier meals to make up the calories. Diets heavy in starch and sugar are linked to a higher risk of colic, laminitis and gastric ulcers. The goal is not simply filling a haynet. It is letting forage carry as much of the nutritional load as it reasonably can.
The Percentage Is a Starting Point, Not a Rule
Ideal intake still depends on body condition, workload, breed, metabolism, forage energy density, pasture access, age, and any pregnancy, lactation or medical condition. An easy keeper on rich forage needs a very different ration from a 600 kg horse in hard work. University of Minnesota Extension gives a practical range: around 1.5% of bodyweight for many overweight or easy-keeping horses, around 2% for the average horse, and up to 2.5% for some hard keepers.
Do Not Count Flakes, and Do Not Forget Waste
"Four flakes a day" is not a unit of weight. Bale compression, grass species and cut all change what a flake actually weighs, so weighing hay, even occasionally, gives a far more honest picture than counting flakes. The same goes for waste: if 12 kg goes into the net and 2 kg ends up trampled into the bedding by morning, the horse ate closer to 10 kg. That gap matters most exactly when intake is already close to the minimum.
Why We Test Every Batch
None of this works without knowing what is actually in the hay. Protein, sugar and energy content cannot be judged by colour or smell, which is why every Prime Hay batch carries its own laboratory analysis rather than a generic average. The current Meadow Hay report:
- Dry matter: 88%
- Crude protein: 8.1% DM
- NSC: 4.5% DM
- Digestible energy: 1.86 Mcal per kg DM
- NDF: 62% DM
- ADF: 41% DM
- Calcium to phosphorus ratio: 1.9:1
These are the same numbers behind the reference-horse calculations on our Science of Feeding page, and the same ones used in the feeding calculator, so a ration built from them reflects the actual batch a horse is eating, not a textbook average.
The Question Worth Asking
Not "how much hay am I feeding," but "how much forage dry matter is my horse actually eating, and what does that forage provide." Quantity and quality only tell the full story together.