A Casein Hydrolysate Does Not Enhance Ileal Endogenous Protein Flows Compared With the Parent Intact Casein When Fed to Growing Pigs

BACKGROUND: The form of dietary nitrogen (free peptides or intact proteins) may influence the amount of endogenous amino acids found at the terminal ileum of the pig, and it has been speculated that hydrolyzed dietary protein may lead to increased endogenous amino acids. OBJECTIVE: To compare the effect of dietary free peptides on ileal endogenous nitrogen and amino acid flows [ileal endogenous nitrogen flow (ENFL), ileal endogenous amino acid flow (EAAFL)] with that of peptides released naturally from dietary protein during digestion, from the same intact parent protein source. METHODS: Six pigs (mean body weight: 34 kg) were equipped with a postvalve T-caecum cannula. Semisynthetic test diets contained the same (15)N-labeled intact casein (C) or hydrolyzed casein (HC). Pigs received the test diets every sixth day and the corresponding unlabeled diets in the intervening 5-d periods. Digesta were pooled from 4 to 10 h postprandially. EAAFL and ENFL, calculated with reference to the dietary marker titanium dioxide, were determined by isotope dilution for C and HC. RESULTS: Ileal EAAFL and ENFL (mean flows n = 5 of 1828 and 1912 μg/g of dry matter intake for diets HC and C, respectively) did not differ (P > 0.05) between pigs fed HC and C. Centrifugation and ultrafiltration of the HC digesta allowed an estimation of label recycling into gut endogenous proteins. Some 20% of ileal endogenous protein (diet HC, ultrafiltered digesta) was (15)N-labeled due to tracer recycling. CONCLUSIONS: The administration of a casein hydrolysate had no effect on ileal endogenous protein flows compared with C. There was no evidence of enhanced ileal endogenous protein losses with the HC diet.