The body of animals is greatly affected by the living of the animals. The quality and quantity of their foods, the air they breathe, the water they drink, the work they do, the exposure they suffer, the health they have, the age they are, determine the desirability of animal foods, both as to nutrition and palatability.

The flesh of some very young animals, as veal, is too compact in fiber to be readily separated, so is not easily reached by digestive juices. The lack of fatty tissue in these increases this compactness of fiber. In very old animals fiber is toughened through living, and fatty tissue has usually become excessive. For these reasons, within the age-range of desirable animal food - 3 to 8 years - 4 to 5 gives the best food. The substances present in the young animal may also differ somewhat from those of the older.

The location of the different parts of the animal used for food determines their exposure and exercise. Neck and legs are toughened by their natural use. The interior of the animal, especially under the backbone from the ribs toward the hind legs, is tender, because protected and little exercised. Outside cuts of meat are 2 1/2 times as tough as those from the interior. In young animals this difference is even greater.

Since flavor is developed by exercise of muscle, and tenderness by lack of it, the choice of parts even within the same animal is always somewhat of a choice between flavor and tenderness. Differences of texture and flavor require different treatment to secure from all parts of animals the nourishment they can yield. Expensive, interior, tender cuts of meat have less flavor; it is cooking that develops flavor in these. Inexpensive, exterior, tough cuts have developed flavor through exercise, but cooking must be relied upon to make them tender.