title: 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.
abstract: 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]leucine 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.
authors.affiliation: Faculté Universitaire des Sciences Agronomiques, Zootechnie, Gembloux, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Leterme
authors.forename: A
authors.initials: A
authors.lastname: Théwis
authors.forename: E
authors.initials: E
authors.lastname: François
authors.forename: P
authors.initials: P
authors.lastname: Van Leeuwen
authors.forename: B
authors.initials: B
authors.lastname: Wathelet
authors.forename: J
authors.initials: J
authors.lastname: Huisman
mesh_terms: D000596:Amino Acids / Q000032:analysis / Q000378:metabolism*; D000818:Animals; D001646:Bile / Q000378:metabolism; D004044:Dietary Proteins / Q000032:analysis / Q000378:metabolism*; D004063:Digestion / Q000502:physiology*; D004798:Enzymes / Q000378:metabolism; D007082:Ileum / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism; D008297:Male; D009077:Mucins / Q000378:metabolism; D009584:Nitrogen / Q000097:blood / Q000378:metabolism; D009587:Nitrogen Isotopes; D010179:Pancreas / Q000201:enzymology; D018532:Pisum sativum / Q000737:chemistry / Q000378:metabolism; D013213:Starch / Q000737:chemistry / Q000378:metabolism; D013552:Swine / Q000378:metabolism* / Q000502:physiology; D013997:Time Factors; D014908:Triticum / Q000737:chemistry / Q000378:metabolism
chemical_list: D000596:Amino Acids; D004044:Dietary Proteins; D004798:Enzymes; D009077:Mucins; D009587:Nitrogen Isotopes; D013213:Starch; D007930:Leucine; D009584:Nitrogen