title: Protein recycling in growing rabbits: contribution of microbial lysine to amino acid metabolism.
abstract: To study the absorption of microbial lysine in growing rabbits, a labelled diet (supplemented with (15)NH4Cl) was administered to six animals (group ISOT); a control group (CTRL, four rabbits) received a similar, but unlabelled, diet. Diets were administered for 30 d. An additional group of six animals were fed the unlabelled diet for 20 d and then the labelled diet for 10 d while wearing a neck collar to avoid caecotrophy (group COLL), in order to discriminate it from direct intestinal absorption. At day 30 animals were slaughtered and caecal bacteria and liver samples taken. The (15)N enrichment in amino acids of caecal bacteria and liver were determined by GC-combustion/isotope ratio MS. Lysine showed a higher enrichment in caecal microflora (0.925 atom% excess, APE) than liver (0.215 APE) in group ISOT animals, confirming the double origin of body lysine: microbial and dietary. The COLL group showed a much lower enrichment in tissue lysine (0.007 (se 0.0029) APE for liver). Any enrichment in the latter animals was due to direct absorption of microbial lysine along the digestive tract, since recycling of microbial protein (caecotrophy) was avoided. In such conditions liver enrichment was low, indicating a small direct intestinal absorption. From the ratio of [(15)N]lysine enrichment between liver and bacteria the contribution of microbes to body lysine was estimated at 23 %, with 97 % of this arising through caecotrophy. Absorption of microbial lysine through caecotrophy was 119 (se 4.0) mg/d, compared with 406 (se 1.8) mg/d available from the diet. This study confirms the importance of caecotrophy in rabbit nutrition (15 % of total protein intake).
authors.affiliation: Departamento de Producción Animal y Ciencia de los Alimentos, Facultad de Veterinaria, Miguel Servet 177, Zaragoza 50013, Spain.
authors.forename: Alvaro
authors.initials: A
authors.lastname: Belenguer
authors.forename: Joaquim
authors.initials: J
authors.lastname: Balcells
authors.forename: Jose A
authors.initials: JA
authors.lastname: Guada
authors.forename: Marc
authors.initials: M
authors.lastname: Decoux
authors.forename: Eric
authors.initials: E
authors.lastname: Milne
mesh_terms: D000042:Absorption; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry; D002432:Cecum / Q000378:metabolism / Q000382:microbiology*; D004032:Diet; D004044:Dietary Proteins / Q000378:metabolism*; D004435:Eating / Q000502:physiology; D007408:Intestinal Absorption / Q000502:physiology; D008239:Lysine / Q000378:metabolism / Q000493:pharmacokinetics; D008297:Male; D009584:Nitrogen / Q000378:metabolism; D011817:Rabbits; D011897:Random Allocation; D015430:Weight Gain / Q000502:physiology
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D004044:Dietary Proteins; D008239:Lysine; D009584:Nitrogen