In the first place, we give various kinds of feed stuffs to our animals that they may live. The heart beats all the time, the lungs contract and expand, digestion is taking place, the blood circulates through the body--something must supply force for these acts or the animal dies. This force is derived from food.
In the next place, food is required to keep the body warm. Food in this respect is fuel, and acts in the same way that wood or coal does in the stove. Our bodies are warm all the time, and they are kept warm by the food we eat at mealtime.
Then, in the third place, food is required to enable the body to enlarge--to grow. If you feed a colt just enough to keep it alive and warm, there will be no material present to enable it to grow; hence you must add enough food to form bone and flesh and muscle and hair and fat.
In the fourth place, we feed to produce strength for work. An animal poorly fed cannot do so much work at the plow or on the road as one that receives all the food needed.
Both food and the force produced by it result from the activity of plants. By means of sunlight and moisture a sprouting seed, taking out of the air and soil different elements, grows into a plant. Then, just as the plant feeds on the air and soil to get its growth, so the animal feeds on the plant, to get its growth. Hence, since our animals feed upon plants, we must find out what is in plants in order to know what animal food consists of.
Plants contain protein, carbohydrates, fat, mineral matter, water, and vitamins. You have seen protein compounds like the white of an egg, lean meat, or the gluten of wheat. The bodies of plants do not contain very much protein. On the other hand, all plant seeds contain a good deal of this substance. Animals make use of protein to form new blood, muscles, and organs. Because of the quality of protein, milk is the best food for children and young animals.
The protein in some foods is of poor quality. To insure a well-balanced supply of protein a variety in foods is desirable. Do not rely on a single kind of mill feed, but combine several kinds, such as cotton-seed meal, linseed meal, wheat bran and middlings, gluten, and similar grain by-products. Tankage for young pigs and meat scraps for chickens are high-grade proteins and are of animal origin.