Next Generation Diet Formulation: True Metabolic Availability of Amino Acids in Diets for Pigs

Not all of the dietary amino acid that is included in standardized ileal digestibility is metabolically available for protein synthesis. A rapid method was developed to determine metabolic amino acid availability in feedstuffs for protein synthesis. Using the indicator amino acid oxidation technique, a change in phenylalanine oxidation, which is inversely proportional to protein synthesis, was used to measure the metabolic availability of lysine in feedstuffs compared to that of free lysine, which is fully available. Data regarding several methodological considerations were addressed before this technique was validated, including: adaptation time between test diets, repeatability of measurements, predictability of response to lysine intake, dietary phenylalanine availability and lysine intake sensitivities. In addition, an oral dosing regimen was developed to simplify the facilities required and lower costs further. This isotope dilution method is suitable for the determination of the metabolic availability of amino acids for protein synthesis in a given feedstuff within 2-3 weeks. This method could also be adapted to predict the availability of other economically important amino acids in feedstuffs (ie threonine, methionine, tryptophan). This new approach is an improvement over the chemical methods which are only available for lysine.