Comparison of methods to determine the endogenous amino acid flow at the terminal ileum of the growing rat

Abstract

The aim was to compare a recently developed peptide alimentation method and the protein-free and regression methods for determining endogenous ileal nitrogen (N) and amino acid excretion in the rat, and to apply the endogenous loss estimates to determine the true ileal digestibility of a meat and bone meal (MBM). Preliminary investigations determined the effect of the time of sampling of digesta after a meal (slaughter 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 the amount of digesta collected and the endogenous N excretion for both the EHC and protein-free fed rats. The amount of digesta collected from the terminal 20 cm of ileum and the endogenous N excretion for both the EHC and proteinfree fed rats were greatest and least variable at 3 h post-feeding. In the main study, endogenous ileal amino acid excretions were determined in the growing rat fed an EHC-based diet (n = 6) and with subsequent treatment of the digesta using ultrafiltration or 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 as the sole protein source. For the EHC treatment, the ileal digesta precipitate plus retentate was used to determine the endogenous flows. The ultrafiltration step excludes unabsorbed dietary amino acids from the measure of endogenous loss. Chromic oxide was the reference marker in all diets. The endogenous N flows determined by the protein-free and regression methods were similar but both significantly (P < 0.01) lower than those for rats fed the EHC-based diet.The mean endogenous ileal N flows determined by the peptide alimentation method, the protein-free and regression approaches were 1866, 1103 and 1019 pg g-' freeze 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 coefficients for MBM were considerably higher based on the EHC versus protein-free endogenous flows.

A protein-free diet alters small intestinal architecture and digestive enzyme activities in rats

“…Our data support the view that dietary protein is stimulatory to intestinal mucosa [39] and endogenous protein secretion [7,8].…”

“…The following day, they received a single meal, 3 h before being sacrificed by asphyxia with chloroform followed by exsanguination. This post-prandial time has been considered as optimal for ileal digestibility studies in rats [6,8]. The rats were weighed and their abdomen was opened immediately.…”

“…In baby calves, small intestinal villus-crypt architecture and digestive enzyme activities of the mucosa were drastically reduced with a PF diet [5]. However, literature data in rats are scarce, despite the numerous studies on gut endogenous protein losses in this animal species [6][7][8]. Chronic malnutrition and starvation in rats impair the gross anatomy of the gut, intestinal epithelial crypt cell proliferation (CCPR) and digestive enzyme activities [9][10][11].…”

Significance of endogenous gut nitrogen losses in the nutrition of growing pigs: A review

“…However, various studies have shown that its estimates are not different from those obtained with feeding protein-free diets (e.g. Taverner et al 1981;Furuya and Kaji 1989;Donkoh et al 1995). Furthermore, a basic assumption with the regression method, as well as with feeding protein-free diets, is that there is no relationship between protein intake and ENL.…”

“…In this study, only the recovery of endogenous proline, glycine and total N was affected (reduced) when amino acids rather than saline (control) were administered intravenously to animals fed a proteinfree diet. As indicated by Butts et al (1993a) and Donkoh et al (1995), a protein-free diet may lack the stimulatory effect on endogenous gut protein secretions. This may lead to an underestimation of ENL at the distal ileum and in faeces.…”