Evolution of Methodologies for Assessing Amino Acid Digestibility in Feedstuffs

The formulation of diets based on digestible amino acid allows feeding diets that better
match the animal requirements as compared to those based on total amino acids. In
addition, they maximize protein absorption and synthesis, reduce nitrogen excretion, and
allow the dietary inclusion of alternative feedstuffs. Several methodologies to estimate
amino acid digestibility and endogenous losses in poultry are reported in the literature. The
amino acid digestibility may be influenced by the methodology applied, type of ingredient,
bird age, and dietary nutrients. The feeding of a protein-free diet is the recommended
method to estimate endogenous amino acid losses, but other methods should be studied and
refined to improve the estimates of total endogenous loss (basal and specific losses).
Expressing feedstuff digestible amino acids as standardized or true ileal digestibility is a
matter of semantics. The precision-fed cecectomized rooster method is currently used only
for specific research. Currently, the method using the ileal content of broilers seems to be
the most recommended to determine the standardized/true ileal digestibility of amino acids
in feedstuffs. The availability of standardized/true digestible amino acid values of
feedstuffs and of nutritional requirements allows formulating economically efficient diets
that promote optimal broiler performance.