Animals used for food range from 3 to 8 years of age. (Steer from 4 to 5 years gives the best beef.) The time, care, food that animals require and the difficulty of the preservation of meat make it essentially a more expensive food than those that take less time, attention, care, and expenditure to produce. In general, food from the vegetable kingdom costs less than from the animal. The vegetable kingdom provides the food for the animal. It is, however, the less expensive foods from the vegetable kingdom which are used as foods by animals, that in turn become food for humankind.

Animals, in being more subject to disease than plants, do not supply so large a proportion of food from those produced for food. To this must be added the further facts that all of the animal is not edible (about 1/5 is not) and all parts do not provide equally desirable food. The fore quarters of beef, which are inferior as food to the hind quarters, weigh 1/7 more than the hind quarters. Together these facts make meat expensive, especially the more tender parts. Conditions of commerce still further affect the cost of such foods in very appreciable ways.

Animal food has worked over in it the constituents of the plants animals eat. These thus become available as human food. The edible portions of animal food are more fully digestible than plant foods edible for humankind. Ninety-five per cent of animal protein is digested; only 85 % of vegetable. This is due more to the arrangement of the latter within vegetable fiber than to the chemical difference in plant and animal protein. This, and the fact that animal food contains more protein, makes the excess of such protein in human diet more possible and probable from meat than vegetables. In this respect animal food is concentrated food. This makes little of it advisable. Expense makes but little of it generally available.