The horse is built back-to-front compared with us: a small stomach — no bigger than a handball relative to the body — and an enormous, fermenting hindgut. The stomach is made for small portions almost constantly. The hindgut is a fermentation chamber where billions of microorganisms break down fibre and turn it into energy — up to a third of the horse energy. The microflora is specialised for exactly the feed the horse eats today, so gut care almost always comes down to one thing: slow changes.