Most horses in Portugal & Spain are fed with love, and with guesswork. This page explains exactly how the Prime Hay Nutritionist calculates, which numbers it uses, and why. No marketing maths: the same conservative values we use for our own horses.
The calculator is for every owner, from a retired pony to a Grand Prix horse. It exists because the most common feeding problems we see are invisible for months: a slowly disappearing topline, dull coat, girthiness, "hot" behaviour, loose droppings. Almost never a lack of care, almost always a lack of numbers.
A horse’s needs are surprisingly knowable: protein and energy scale with bodyweight, workload, age and condition. What’s usually unknown is what the hay actually delivers. That is the gap this calculator closes.
| Protein need (500 kg horse) | 675 g/day at rest → 930 g/day top sport |
| Energy need (500 kg horse) | 5.3 EWpa at rest → 8.3 EWpa top sport |
| Forage guideline | ≥ 2.5% of bodyweight per day · ~12.5 kg |
| Never without hay for | more than ~3 hours (gut health) |
Search the internet and every feeding table tells you the same thing: grass hay is “around 10–11% crude protein”. Our laboratory results tell a different story. We test continuously, and even the best hay we find is rarely much above 8%, and the everyday local hay horses actually eat often measures dramatically lower. We have seen batches as low as 2–6%.
And here is the trap: when a hay does test higher in protein, it almost always tests higher in sugar too, because both come from young, lush, fast-grown grass. You don’t get "rich" hay for free; you pay for it in WSC.
| Internet feeding tables assume | ~10–11% protein |
| Best hay in our lab tests | rarely much above 8% |
| Typical local hay we measure | often far lower, down to 2–6% |
| Higher protein usually means | higher sugar as well |
| Prime Hay meadow hay (lab card) | 8–11% CP · WSC < 10% |
| What the calculator uses for our hay | 7%, deliberately below our own lab range |
This is why the calculator never uses generic averages. It calculates with measured, conservative values, and that is also why a horse on unknown local hay so often turns out to be hundreds of grams of protein short while looking “well fed”.
Water-soluble carbohydrates (WSC) drive insulin spikes. For laminitis-prone, EMS and Cushing’s horses, sugar-rich forage is the single biggest daily risk. That is why our meadow hay is guaranteed WSC < 10%, and why the calculator hard-blocks sugary feeds for sensitive horses.
Sugar-rich hay plus a starchy grain concentrate is a double glycemic load. Undigested starch spills into the hindgut, acidifies it, and shows up as ulcers, colic risk, loose droppings and “hot” unrideable behaviour.
Horses are built to burn fibre, slowly and steadily. Low-sugar forage keeps blood sugar flat, the hindgut healthy and the mind calm, which is exactly what sport horses need to perform.
When the ration comes up short on protein, the reflex of the feed industry is: add another scoop. Ours is the opposite: fix the forage first. Alfalfa (lucerne) is a protein-dense forage, 15–18% crude protein, rich in lysine, naturally buffering for the stomach thanks to its calcium.
The calculator swaps, never adds: give 4 kg of alfalfa and it automatically takes 4 kg of meadow hay out, a horse cannot eat more total hay. And it caps alfalfa at 4 kg/day (~⅓ of the ration), because beyond that the calcium–phosphorus balance tips.
| Alfalfa crude protein | 15–18%, 2× the best grass hay |
| How it’s added | Swapped 1-for-1 against meadow hay |
| Maximum we advise | 4 kg/day · ~⅓ of total forage |
| Cost of the swap | only ~€7–15/month |
| Automatic for | hard & top-sport workloads |
Once forage covers protein and energy, a horse still needs vitamins, minerals and trace elements that even the best hay cannot fully supply. That, and only that, is what the daily bucket is for. So the calculator advises a small (~1 kg), mild, fibre-based feed, and it deliberately favours grain-free and GMO-free options: no starch overload for a job that starch cannot do, no cheap fillers, no genetically modified raw materials. Not for calories, for completeness.
The nr. 1 issue. Owners know their concentrate to the gram, and have no idea what 90% of the diet (the hay) delivers. Unknown hay is unmanaged nutrition.
Poor hay “compensated” with 3–4 kg of grain concentrate. The gap closes on paper, and opens the door to ulcers, acidosis and hot behaviour.
Lush, rich-looking hay chosen for sensitive horses, exactly the hay most likely to be high in sugar. Colour tells you nothing; a lab report does.
On 2–6% hay a 500 kg horse can be 300–500 g of protein short every single day. You see it months later: topline gone, coat dull, slow recovery.
Senior muesli for a 10-year-old, breeding feed for a leisure horse, “calm” mixes full of starch. The label decides, not the horse’s actual needs.
Two feedings a day and an empty net by 21:00. A horse’s stomach produces acid 24/7, more than ~3 hours without forage is how ulcers start.
| 1 | Needs, protein (g) & energy (EWpa) from bodyweight × workload, corrected for age, condition and metabolism. |
| 2 | Forage base, 2.5% of bodyweight in hay, using measured values (our hay counted at a conservative 7% protein). |
| 3 | Gap check, whatever protein/energy the forage doesn’t cover becomes the target for the rest of the ration. |
| 4 | Alfalfa swap, for hard work the gap is closed forage-first, capped at 4 kg, swapped not added. |
| 5 | Mild feed, ~1 kg grain-free/GMO-free muesli for vitamins & minerals; sugary and unsuitable feeds are hard-filtered per horse. |
| 6 | Score, the 0–10 score weighs forage share, coverage, sugar & starch load, gut health and micronutrients. |
Conservative on purpose. Everywhere the engine has a choice, it takes the cautious number: the lowest guaranteed lab values for our own hay, a safety margin on feed amounts, and hard blocks instead of warnings for sensitive horses. A feeding plan should never be optimistic.
Estimates are for guidance, always monitor your horse’s condition and consult your vet for medical decisions.
Join 450+ horse owners across Portugal & Spain getting expert forage advice, early delivery slots and member-only offers.
No spam, just hay. Unsubscribe anytime. Prefer WhatsApp updates? Message us.
