If you have ever wondered why the EVN feeding plan for your endurance horse looks different from what many yards do by default — this explains the reasoning behind each key decision. No jargon, just the 'why'.
1. Why fat, not starch
Most commercial horse feeds are built around starch — the energy in cereals. Starch is a fast fuel. It works well for sprint athletes: racehorses over a mile, showjumpers clearing a course in three minutes. Your endurance horse is not a sprint athlete. Over 80 or 160 kilometres, the primary fuel is fat — the fat in the horse's own body and the fat in the diet. Fat provides roughly twice as much energy per gram as starch, and the body can access it steadily over many hours, without the peaks and crashes of high-starch feeding.
Feeding an endurance horse mainly on starch is like a runner trying to complete a marathon on energy drinks. It works for a while — then it doesn't. Your EVN plan includes oil or a fat-containing feed as the main energy source. That is deliberate: the body needs about 8–12 weeks to learn to use fat efficiently as fuel — so we start fat well before the season, not a week before the first ride.
2. Why so much hay
The horse's large colon is enormous: about 3–4 metres long, holding 80–100 litres of water and digesting fibre. It is, in effect, a built-in water tank. When the horse eats hay, the fibre in the large colon holds water; as the horse works and loses fluid, the body draws on this reservoir. Hay is not ballast — hay is fluid management. (See 'Your horse's built-in water tank'.)
3. Why electrolytes with water — never without
Horse sweat is saltier than the fluid in the blood vessels. Every time your horse sweats, it loses proportionally more salt than water. Over a long ride the body becomes relatively salt-depleted. Replace that loss with plain water alone — no salt — and you dilute the remaining salt further (dilutional imbalance), which makes things worse. So we use electrolytes with sodium chloride as the main ingredient: they replace what the horse is actually losing.
But — critically — electrolytes must always be given with water. A paste without water draws fluid from the gut lining into the gut and temporarily worsens dehydration. The EVN rule is absolute: electrolytes only when water is available and the horse has already drunk. That is why the vet gate order is cool, then water, then hay — and only then electrolytes. The order is not arbitrary; it follows the physiology.
4. Why we do not use alkalinising supplements
You may have heard of 'bicarbonate loading' (baking soda) as a performance aid — the idea that it buffers the lactic acid built up in intense exercise. For endurance horses this is completely wrong, and potentially dangerous. Sprint horses at maximum intensity produce lots of lactic acid; their blood turns acidic, and bicarbonate neutralises it. Endurance horses work for hours at moderate intensity and do not produce that lactic acid — on the contrary, over a long ride the blood becomes slightly too alkaline (alkalosis).
Adding bicarbonate to a horse already tending toward alkalosis makes it worse: alkalosis impairs muscle function and calcium regulation and contributes to the dangerous 'thumps'. It is also on the FEI prohibited list for endurance. If anyone — another rider, yard manager or feed rep — asks whether your horse should get bicarbonate or any alkalinising supplement, the answer is no. Unsure about a product? Check with EVN before giving it.
This is general information. It does not replace the individual feeding plan your EVN vet prepares for your horse after assessing it.