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 o f extrapolating the ileal losses of endogenous amino acids (AA) with l inear relationships between the distal heal outputs and dietary inputs of AA. Six barrows, average initial body weight 35 kg, were fitted wi th 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 containin g six levels of crude protein (CP) and AA from soya bean meal (4, 8, 1 2, 16, 20 and 24% CP, respectively) were formulated. Chromic oxide (4 g kg(-1) diet) was included as the digestibility marker. Each experime ntal 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 aff ected the linearity and caused large differences in the extrapolated l evels of heal endogenous AA. Therefore, the design of a suitable range of graded dietary levels of AA is the most important methodological c onsideration for the determination of endogenous AA losses and the tru e 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, i n 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, th e levels of endogenous AA extrapolated with the linear relationships b etween the heal outputs and dietary inputs of AA were very close to th e values estimated with the linear relationships between the dietary c ontents of apparent ileal digestible and total AA, suggesting that bot h models of linear relationships can be used as the regression analysi s technique for determination of ileal losses of endogenous AA and tru e heal digestibility values of AA in feedstuffs for pigs.