In order to obtain an adequate supply of material for furnishing energy and for repairing bodily waste, the food must be sufficient in quantity and composition.

The measure of a horse's appetite is by weight, rather than by bulk. As the feeding value of corn is more than double that of hay, we can, by substituting corn for a portion of the hay, increase the amount of nutrition in the food, without exceeding the limit of appetite. Thus, a daily ration of 19 lbs. of corn and 12 lbs. of hay (total = 31 lbs.) would be theoretically equivalent to at least one of 50 lbs. of hay, which would be a quantity far exceeding the eating capacity of an ordinary horse. The consumption of hay takes more time than that of corn (p. 79); it entails a greater loss of energy in chewing and digesting it (p. 99); and causes a horse to drink more water (p. 99), and consequently impedes his breathing powers to a greater extent, by increasing the weight and size of the contents of his stomach and intestines. Hence the necessity of corn for working horses.

As regards the composition of food, we find that the harder the work, the more starch and fat does a horse need, and that little or no increase is required in nitrogenous matter. Consequently, maize is an admirable food for hard-working adult horses; although, as we have seen, it is a poor one for growing animals.