They are then absorbed and transported by the blood to the cells which assemble these amino acids into body proteins. Body proteins are used in the construction of body tissue. Tissues which mainly consist of protein are muscles, nerves, cartilage, skin, feathers and beak. The tag on a bag of poultry feed lists the percent crude protein. This tells you only the percentage guarantee and does not indicate the quality of the protein used.
Protein quality is based on the presence of essential amino acids in the feed ingredients.
In developing a poultry ration, the nutritionist will include a variety of feedstuffs which are high in protein. The reason for this is that no single feedstuff is able to provide all the amino acids that are needed. But when the proteins from different feedstuffs are used, the ration can be formulated to contain all the necessary amino acids. The main sources of protein in poultry rations are animal proteins such as fish meal, meat and bone meal, and plant proteins, such as soybean meal, cottonseed meal and corn gluten meal. The mineral portion of the feed is inorganic matter.