THE N-15-ISOTOPE DILUTION METHOD FOR DETERMINING ILEAL ENDOGENOUS NITROGEN-EXCRETION IN THE YOUNG (10 KG LIVEWEIGHT) PIG

A study was conducted with four crossbred 5-week-old castrated male pi gs at an average body weight of 10 kg to determine the endogenous amin o acid and nitrogen flows at the terminal ileum using the peptide alim entation and N-15-isotope dilution methods. The pigs were fitted with a post-valvular T caecal cannula and two indwelling blood catheters. T hey were fed a cornstarch-based semisynthetic diet formulated to conta in enzymically hydrolysed casein (EHC) as the sole source of nitrogen at twice their maintenance requirement for energy. Digesta were centri fuged and ultrafiltrated after collection and the precipitate plus ret entate fraction (mol wt > 10 000) was used to determine the endogenous amino acid and nitrogen flows. To estimate the endogenous N flow at t he terminal ileum of these EHC-fed pigs using the N-15-isotope dilutio n method a constant 10 day N-15-leucine infusion was performed at a da ily rate of 5.04 mg of N-15-leucine (95% N-15 enrichment) kg(-1) body weight. The mean N-15-enrichments enrichments above background for the trichloroacetic acid soluble blood plasma and ileal digesta nitrogen pools were 0.0249 and 0.0178, respectively. There were no statisticall y significant differences for N-15-enrichment excess between the days of ileal digesta collection. The results demonstrated that glutamic ac id, aspartic acid, proline and serine formed about 50% of the total il eal endogenous amino acid flow. The total daily amount of endogenous a mino acid flow at the terminal ileum was 6.2 g day(-1). The endogenous ileal N flows determined with the peptide alimentation and the N-15-i sotope dilution methods were similar (P = 0.40) at 1.37 and 1.17 g day (-1), respectively. Endogenous N as a proportion of total N flow passi ng the terminal ileum was 83% and 72% for the peptide alimentation and the N-15-isotope dilution method, respectively. The study provides so me support for application of the N-15-isotope dilution method with pi gs.