Nitrogen, amino acid and starch absorption and endogenous nitrogen and amino acid excretion in chicks fed on diets containing maize as the sole source of protein

Abstract

The endogenous fraction of nitrogen (N) and amino acid (AA) in the faeces (excreta N  N of uric acid) of maize-fed chicks was calculated to determine true absorption values from the apparent values. The diets contained magnesium ferrite as a marker and various levels of maize as the sole source of protein; an N-free diet of maize starch only was also tested. The true absorption values (N=0.77, AA=0.37–0.85) calculated from the slope of the regression line were higher than the apparent ones (N=0.67, AA=0.26–0.81). The eliminated endogenous fraction, which is represented by the intercept of the regression line, was lower than the values of N and AA determined in the faeces of the N-free diet. As a result, the so-called “true” N absorption values were too high (1.09–1.12). In a second experiment with only one dietary level of maize there was a large difference between the N and AA apparent absorption values if determined in the lower ileum (N=0.81, AA=0.57–0.88) or in the faeces (N=0.57, AA=0.22–0.79), pointing to an endogenous fraction which is greater in the faeces than in the lower ileum. The individual AA absorption values differed distinctly from one another in all cases and were not represented by the apparent and true N absorption values. The high values of starch absorption from maize are 0.997 (excreta) and 0.983 (lower ileum), emphasizing the difference for N and the variability in both apparent and true AA absorption values determined in the lower ileum or faeces.