Determination of true ileal amino acid digestibility in feedstuffs for pigs with the linear relationships between distal ileal outputs and dietary inputs of amino acids

This study was carried out to investigate the methodological aspects of extrapolating the ileal losses of endogenous amino acids (AA) with linear relationships between the distal heal outputs and dietary inputs of AA. Six barrows, average initial body weight 35 kg, were fitted with a simple T-cannula at the distal ileum and fed six diets according to a 6 x 6 Latin square design. Six maize starch-based diets containing six levels of crude protein (CP) and AA from soya bean meal (4, 8, 12, 16, 20 and 24% CP, respectively) were formulated. Chromic oxide (4 g kg(-1) diet) was included as the digestibility marker. Each experimental period consisted of 8 days. Ileal digesta were collected, at 2 h intervals, for a total of 24 h during days 7 and 8. There were strong linear relationships (P < 0.01) between the ileal outputs and dietary inputs of AA. Differences in ranges of graded dietary levels of AA affected the linearity and caused large differences in the extrapolated levels of heal endogenous AA. Therefore, the design of a suitable range of graded dietary levels of AA is the most important methodological consideration for the determination of endogenous AA losses and the true heal digestibility values of AA with the linear relationship. For CP and the essential AA, the true heal digestibility values (%) in soya bean meal and the ileal endogenous losses (g kg-l dry matter intake, in parentheses) were as follows: CP, 89.4 (16.4); arginine, 96.1 (0.68); histidine, 92.4 (0.24); isoleucine, 91.7 (0.45); leucine, 90.7 (0.69); lysine, 90.5 (0.48); methionine, 93.6 (0.13); phenylalanine, 92.5 (0.38); threonine, 86.5 (0.71) and valine, 90.3 (0.56). Furthermore, the levels of endogenous AA extrapolated with the linear relationships between the heal outputs and dietary inputs of AA were very close to the values estimated with the linear relationships between the dietary contents of apparent ileal digestible and total AA, suggesting that both models of linear relationships can be used as the regression analysis technique for determination of ileal losses of endogenous AA and true heal digestibility values of AA in feedstuffs for pigs.