A confusing aspect of nutrition is that all types of protein do not have the same nutritive value. As an example, lets consider the different protein components of the animal body. Such constituents as horns, nails, and feathers are composed of protein just as are the fleshy parts of the body. However, the nutritive value of meat is far, far superior to that of the same amount of protein originating from these hard tissues. Protein is composed of combinations of different individual amino acids and the specific amino acid composition of a protein determines its nutritional quality.
Some amino acids are much more important than others to the proper nutrition of the bird.
Lysine and methionine are usually considered the most critical amino acids for poultry. In diets for the backyard flock, if soybean meal is the primary source of protein, supplemental lysine may not be needed. However, supplemental methionine is usually needed to ensure that the quality of the protein in the ration is adequate for optimum production, even when the quantity of protein appears adequate on the feed label. Often times, one hears the terms plant protein and animal protein. The implication of these terms is obvious.