In practice, L-Threonine is the second limiting amino acid for pigs and the third for poultry.

Once the lysine supply is optimised, the next limiting amino acid is the one that limits protein synthesis the most.

L-Lysine is the most important amino acid for monogastric species, as it is the first limiting amino acid for pigs and the second limiting amino acid for poultry.

Proteins are evaluated according to the formula: (mg of limiting amino acid in 1 g of test protein / mg of same amino acid in 1 g of reference protein) x fecal true digestibility percentage.

L-threonine is considering like the 2nd (after lysine) or 3 rd (after lysine and methionine) limiting amino acid, depending on publications.

The formula for calculating the PDCAAS percentage is: (mg of limiting amino acid in 1 g of test protein / mg of same amino acid in 1 g of reference protein) x fecal true digestibility percentage.[2]

While animal sources of protein contain all the essential amino acids, plant sources lack one or more, called the limiting amino acid.

If there is a lack of even one of these (limiting amino acid), the protein synthesis becomes ineffective (in the worst case) or in any case less efficient than it has potential to be.