Oxidation of essential amino acids by the ovine gastrointestinal tract

Abstract

It is not known if the ruminant animal gastrointestinal tract (GIT) can oxidise essential amino acids (AA) other than leucine. Therefore, the oxidation of four essential AA (leucine, lysine, methionine and phenylalanine), supplied systemically as labelled 1-¹³C forms, was monitored across the mesenteric-drained viscera (MDV; small intestine) and portal-drained viscera (PDV; total GIT), as part of a 4×4 Latin square design, in four wether sheep (35–45 kg) fed at 1·4 × maintenance. Oxidation was assessed primarily by appearance of¹³CO_2,corrected for sequestration of [¹³C]bicarbonate. The GIT contributed 25 % (PPPP<0·001) between AA, e.g. phenylalanine (0·81), lysine (0·71), methionine (0·67), leucine (0·56), histidine (0·71), threonine (0·63) and tryptophan (0·48). These differences probably reflect incomplete re-absorption of endogenous secretions and, together with the varied oxidative losses measured, will alter the pattern of AA net supply to the rest of the animal.