Comparison of different methods for determination of the duodenal and ileal flows of endogenous nitrogen and amino acids in growing goats

Abstract

The objective of the present study was to compare the isotope dilution, the difference and the amino acid profile (AAP) methods for the quantification of duodenal and ileal flows of endogenous nitrogen (N) and amino acids (AA) in growing goats. Nine growing goats were fed the same diet containing maize stover, ground corn and soybean meal. The duodenal flow of endogenous N determined by the isotope dilution method was significantly (p < 0.01) higher than that determined by the difference and AAP methods, while there was no difference between the difference and the AAP methods. The duodenal flows of individual endogenous AA determined by the isotope dilution method exceed those determined by the difference and the AAP method by 10 to 106%. The endogenous flow at the ileum determined by the isotope dilution method was not significantly different to those determined by the water-soluble method, but tended to be lower for N and all amino acids. It is concluded that the difference method and AAP method underestimate the duodenal flow of endogenous N and AA compared to the isotope dilution method.