COMPARISON OF METHODS TO DETERMINE THE ENDOGENOUS AMINO-ACID FLOW AT THE TERMINAL ILEUM OF THE GROWING RAT

The aim was to compare a recently developed peptide alimentation metho d and the protein-free and regression methods for determining endogeno us ileal nitrogen (N) and amino acid excretion in the rat, and to appl y the endogenous loss estimates to determine the true ileal digestibil ity of a meat and bone meal (MBM). Preliminary investigations determin ed the effect of the time of sampling of digesta after a meal (slaught er method) for rats given a protein-free or an enzymically hydrolysed casein (EHC) based diet, on ileal digesta and endogenous N excretion. There was a significant (P < 0.05) effect of the time of sampling on t he amount of digesta collected and the endogenous N excretion for both the EHC and protein-free fed rats. The amount of digesta collected fr om the terminal 20 cm of ileum and the endogenous N excretion for both the EHC and protein-free fed rats were greatest and least variable at 3 h post-feeding. In the main study, endogenous ileal amino acid excr etions were determined in the growing rat fed an EHC-based diet (n = 6 ) and with subsequent treatment of the digesta using ultrafiltration o r in six rats given a protein-free diet or by extrapolation from data for 30 animals given five diets which contained graded levels of MBM a s the sole protein source. For the EHC treatment, the ileal digesta pr ecipitate plus retentate was used to determine the endogenous flows. T he ultrafiltration step excludes unabsorbed dietary amino acids from t he measure of endogenous loss. Chromic oxide was the reference marker in all diets. The endogenous N flows determined by the protein-free an d regression methods were similar but both significantly (P < 0.01) lo wer than those for rats fed the EHC-based diet. The mean endogenous il eal N flows determined by the peptide alimentation method, the protein -free and regression approaches were 1866, 1103 and 1019 mu g g(-1) fr eeze dry matter intake, respectively. The endogenous amino acid flows at the terminal ileum were lower when determined using the traditional protein-free or regression methods. The true ileal digestibility coef ficients for MBM were considerably higher based on the EHC versus prot ein-free endogenous flows.