The concept of digestible amino acids in diet formulation for pigs

There is sufficient evidence that ileal rather than fecal amino acid digestibility values provide a more reliable estimate of protein digestion and amino acid absorption. In addition to differences in ileal amino acid digestibility values between feedstuffs there are large differences in ileal amino acid digestibility values within the same feedstuff. Furthermore, in addition to different processing conditions and inherent differences among samples of the same feedstuff, a large proportion of this variation can be attributed to different methodological approaches. In order to reduce the within variation associated with different methods for determination, methods specifically 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 threshold levels, after which apparent digestibility values become independent of the dietary amino acid levels. The correction for non-specific endogenous protein and amino acid recoveries in ileal digesta allow for the transformation of apparent digestibility to standardised ileal digestibility values. The non-specific recoveries are related to the dry matter intake but independent of the type of feedstuff. In principle, standardised digestibility values should be the preferred approach in protein evaluation because these values reflect a fundamental property of the feedstuffs being independent of experimental conditions. However, estimates of endogenous recoveries are still confounded by the method used for determination, and further research is warranted in this area.  2000 Elsevier Science B.V. All rights reserved.