Amino acids are the building blocks of proteins and polypeptides that are the major component of animals' muscles and tissues. Amino acids also form an important component in some fluids such as milk. In addition to being building blocks of body proteins, amino acids play a significant role in various important biochemical and metabolic processes in the cells of animals. The composition of amino acids in feeds is very variable, so it is important to closely monitor feed quality to ensure that animals are consuming appropriate amounts of essential amino acids to maintain their health and productivity while maximizing profitability. The essential amino acids for poultry and livestock are : lysine, methionine, threonine, tryptophan and valine.