EVALUATION OF THE N-15-ISOTOPE DILUTION TECHNIQUE FOR DETERMINING THERECOVERY OF ENDOGENOUS PROTEIN IN ILEAL DIGESTA OF PIGS - EFFECT OF THE PATTERN OF BLOOD-SAMPLING, PRECURSOR POOLS, AND ISOTOPE-DILUTION TECHNIQUE

The N-15-enrichments (atom percentage excess) were determined in the p lasma free amino acids of blood samples taken at the time of feeding a nd in samples taken hourly and pooled over 12 h, as well as in ileal d igesta, crude mucin, and bacteria collected at the distal ileum of pig s fed barley while continuously administered [N-15]leucine intravenous ly. The branched-chain amino acids were the only indispensable amino a cids to exhibit incorporation of N-15 (P < .05). All dispensable amino acids exhibited some incorporation. Enrichments in free leucine and a lanine were higher (P < .02) in blood samples taken at the time of fee ding, compared to those in pooled blood samples, resulting in an under estimation of the endogenous ileal recoveries of these amino acids. En richments in amino acids in crude mucin were usually similar to those in pooled plasma samples, providing some support for the use of plasma free amino acids to estimate enrichments in endogenous amino acids in ileal digesta. Enrichments in bacteria were not different (P > .05) f rom those in ileal digesta. The recoveries of endogenous amino acids i n ileal digesta determined with the [N-15]leucine and N-15-amino acid dilution techniques demonstrate the overestimation of these criteria w ith the N-15-isotope dilution technique, applied in its current form, and suggest that modifications in the composition of endogenous protei n can occur when pigs are fed protein-containing diets. This study sup ports the use of N-15-isotope dilution techniques, with modifications, for determining the recovery of endogenous protein in ileal digesta o f pigs fed protein-containing diets.