Protein recycling in growing rabbits: contribution of microbial lysine to amino acid metabolism

• Published in: British journal of nutrition Vol. 94; no. 5; pp. 763 - 770
• Main Authors: Belenguer, Álvaro, Balcells, Joaquim, Guada, Jose A., Decoux, Marc, Milne, Eric
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 01.11.2005
• Subjects: 15N kinetics; Absorption; amino acid metabolism; Amino acids; Amino Acids - metabolism; animal growth; Animals; Bacteria; Bacterial Proteins - chemistry; Biological and medical sciences; Caecotrophy; cecum; Cecum - metabolism; Cecum - microbiology; Diet; dietary protein; Dietary Proteins - metabolism; Eating - physiology; Feeding. Feeding behavior; Fundamental and applied biological sciences. Psychology; intestinal absorption; Intestinal Absorption - physiology; Liver; lysine; Lysine - metabolism; Lysine - pharmacokinetics; Male; Metabolism; Microbial lysine; microbial proteins; Nitrogen - metabolism; nutrient partitioning; Nutrition research; Proteins; Rabbit; Rabbits; Random Allocation; rumen fermentation; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Weight Gain - physiology; Spain; Caecotrophy; Rabbit; Microbial lysine; 15N kinetics; Growth; Supplemented diet; Lagomorpha; Metabolism; Protein; Feeding; Rabbit: Caecotrophy: Microbial lysine: 15N kinetics; Vertebrata; Mammalia; Lysine; Aminoacid; Animal; Kinetics; Recycling
• ISSN: 0007-1145; 1475-2662
• DOI: 10.1079/BJN20051508

To study the absorption of microbial lysine in growing rabbits, a labelled diet (supplemented with 15NH4Cl) was administered to six animals (group ISOT); a control group (CTRL, four rabbits) received a similar, but unlabelled, diet. Diets were administered for 30d. An additional group of six animals were fed the unlabelled diet for 20d and then the labelled diet for 10d 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 15N 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 [15N]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).