It also seals the grain particles to reduce their oxidation during storage. The limited starch digesting enzyme capacity of the small intestine is then able to more efficiently attack the bonds between the long chain sugars, greatly improving digestion of the starch. Cooked corn becomes a cool energy feed rather than heating feed for a horse. Cracking grains does not significantly increase digestibility in the small intestine, but opening raw grain hastens the oxidation of fats and vitamins in the grain. Basically, their digestive processes and efficiencies are relative to their size and digestive tract length and volume.
Some horses have a more efficient metabolic function than others, requiring less feed.
However, a nervy horse may expend more energy and need more feed than a quieter horse. The same balances of hard feed to hay should be maintained to ensure efficient digestive function, but for the same amount of work, smaller horses may need a higher energy density because their appetite and capacity for bulk may be limited for an equal amount of energy expenditure. A standardbred racehorse or an Arabian endurance horse often has a smaller frame and gut capacity than a larger thoroughbred and requires a higher energy density in the ration for this reason. A 500kg mare feeding a foal needs the same amount of energy each day as a racing thoroughbred, but more protein, calcium and trace-minerals. Minis are a scaled down horse in most respects, but have a correspondingly shorter small intestine.