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The use of 15N-labeled dietary proteins for determining true ileal amino acid digestibilities is limited by their rapid recycling in the endogenous secretions of pigs

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Author: Leterme, P. · Théwis, A. · François, E. · Leeuwen, P. van · Wathelet, B. · Huisman, J.
Institution: Instituut voor Landbouwkundig Onderzoek en Biochemische Produkten TNO
Source:Journal of Nutrition, 9, 126, 2188-2198
Identifier: 233433
Keywords: Biology · 15N · Endogenous · Ileal digestibility · Pigs · Amino acid · Amino acid blood level · Amino acid metabolism · Animal experiment · Digestion · Nonhuman · Protein secretion · Small intestine absorption · Swine · Animal · Blood · Chemistry · Enzymology · Metabolism · Physiology · Protein intake · Time · Wheat · Amino Acids · Animals · Bile · Dietary Proteins · Digestion · Enzymes · Ileum · Leucine · Male · Mucins · Nitrogen · Nitrogen Isotopes · Pancreas · Peas · Starch · Swine · Time Factors · Triticum


We assessed the use of 15N-labeled dietary proteins as a possible tool for the determination of the true ileal amino acid (AA) digestibility in pigs. The first experiment was designed to study the dietary N excretion pattern at the ileum subsequent to the ingestion of a single 15N-labeled meal. In a second experiment, we compared ileal endogenous AA outputs and true AA digestibility estimates obtained in pigs ingesting 15N-labeled dietary proteins in a single meal vs. intravenous infusion of [15N]Ieucine for 10 d during the ingestion of a pea-based diet and a protein-free starch diet. The proportion of endogenous N found in the ileal digesta differed when the label was delivered orally (50%) vs. intravenously (72%) and changed with time. As a consequence, the true ileal AA digestibilities measured with labeled diets were lower. A third experiment demonstrated that this was due to the rapid recycling of labeled dietary N in endogenous moieties, because 15N was found in blood within 10 min of consuming the labeled meal, within 50 min of consumption in pancreatic enzymes, 90 min in bile and 4 h in ileal mucins. We conclude that the use of 15N-labeled meals for determination of true ileal AA digestibilities is limited by the fast recycling of dietary N in endogenous secretions following a single 15N-labeled meal. The accuracy of results will depend on meaningful estimates of AA flow during a limited period and accurate estimates of 15N in AA.