The concept of digestible amino acids in diet formulation for pigs

There is sufficient evidence that ileal rather than fecal amino acid digest ibility values provide a more reliable estimate of protein digestion and am ino acid absorption. In addition to differences in ileal amino acid digesti bility values between feedstuffs there are large differences in ileal amino acid digestibility values within the same feedstuff. Furthermore, in addit ion to different processing conditions and inherent differences among sampl es of the same feedstuff, a large proportion of this variation can be attri buted to different methodological approaches. In order to reduce the within variation associated with different methods for determination, methods spe cifically suitable for different feedstuffs are recommended. Differences in dietary amino acid levels are likely to be the largest single contributor to the variation in ileal amino acid digestibility values. Therefore, it is suggested to determine their plateau values, also referred to as dietary t hreshold levels, after which apparent digestibility values become independe nt of the dietary amino acid levels. The correction for non-specific endoge nous protein and amino acid recoveries in ileal digesta allow for the trans formation of apparent digestibility to standardised ileal digestibility val ues. The non-specific recoveries are related to the dry matter intake but i ndependent of the type of feedstuff. In principle, standardised digestibili ty values should be the preferred approach in protein evaluation because th ese values reflect a fundamental property of the feedstuffs being independe nt of experimental conditions. However, estimates of endogenous recoveries are still confounded by the method used for determination, and further rese arch is warranted in this area. (C) 2000 Elsevier Science B.V. All rights r eserved.