The principal component of living organisms is protein, which is composed of around 20 amino acids. Some of these amino acids are nonessential amino acids, which are synthesized inside the body, and some of these amino acids are essential amino acids, which should be supplemented to the body from an outside source. Threonine is one of the essential amino acids needed in comparably large amounts by living organisms. Particularly in Europe where large amounts of cereal grains and other feedstuffs are used in swine formulations, threonine may become the first limiting amino acid. This would indicated a positive response to increasing levels of lysine may also be limited by a possible deficiency of threonine. Threonine is not found in sufficient quantities all cereal grains, especially wheat and barley(which provide only 70~80% of the optimum amount of threonine as recommended by the A.R.C.). It is now generally accepted that the requirement for each essential amino acid is proportionally linked to the requirement for lysine. Accordingly, you should consider supplementing with threonine when adding lysine to your feed formulations.