Effect of Oral and Parenteral N Nutrition vs N‐Free Nutrition on the Endogenous Amino Acid Flow at the Ileum of the Pig*

Two methods were tested for suppressing the depressive effect of N-free diets on the digestive secretions in pigs : the blood perfusion of amino acids (AA) or the peptide alimentation method. In the latter, enzymically hydrolysed casein (EHC), composed of oligopeptides and free AA, was used as the source of nitrogen. The unabsorbed dietary N molecules were discarded from the ileal digesta by ultrafiltration or gel filtration, assuming that the endogenous fraction did not contain significant amounts of small molecules. The AA supply by blood perfusion had no effect on the ileal endogenous AA losses (8.0 g AA kg -1 DM intake) in growing pigs (±50 kg), compared with the N-free diet alone (8.3 g), whereas the EHC supplementation significantly increased them (18.0 g). The increase was due to both endogenous and dietary N. The presence of unabsorbed dietary AA in the ileal digesta was confirmed by the AA profile of the soluble molecules with a very low molecular mass ( < 3 kDa), which was close to that of EHC. Both ultrafiltration (cut-offs of 3 or 10 kDa) and gel filtration methods, utilised to discard the remaining dietary molecules, also eliminated a significant proportion of endogenous AA.