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Nutrient Metabolism

Route of Tracer Administration Does Not Affect Ileal Endogenous Nitrogen Recovery Measured with the ¹⁵N-Isotope Dilution Technique in Pigs Fed Rapidly Digestible Diets^1,2

C. A. (Carina) Steendam³, Martin W. A. Verstegen, Seerp Tamminga, Huug Boer, Marianne van ’t End, Berthe Verstappen^*, William R. Caine and G. Henk Visser^*

Animal Nutrition Group, Wageningen Institute of Animal Sciences (WIAS), Wageningen University and Research Centre, 6700 AH Wageningen, The Netherlands; Olds College Centre for Innovation, Olds, AB, Canada, T4H 1R6; and ^* Centre for Isotope Research (CIO), University Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands

³To whom correspondence should be addressed. E-mail: Carina.Steendam{at}wur.nl.

The ¹⁵N-isotope dilution technique (¹⁵N-IDT), with either pulse-dose oral administration or continuous i.v. administration of [¹⁵N]-L-leucine (carotid artery), both at 5 mg/(kg body weight · d), was used to measure ileal (postvalve T-cecum cannula) endogenous nitrogen recovery (ENR) in pigs (9 ± 0.6 kg). Diets were cornstarch, enzyme-hydrolyzed casein with no (control) or high (4%) content of quebracho extract (Schinopsis spp.) rich in condensed tannins. Blood was sampled from a catheter in the external jugular vein. Mean plasma ¹⁵N-enrichment at d 8–10 was higher (P = 0.0009) after i.v. than after oral administration [0.0356 vs. 0.0379 atom% excess (APE)]. Plasma ¹⁵N-enrichment for i.v. infused pigs was 0.01117 APE higher (P < 0.0001) and for orally dosed pigs 0.0081 APE lower (P < 0.0001) at 11 h postprandial compared with 1 h postprandial. Apparent ileal N digestibility was higher (P < 0.0001) for the control (85.5%) than for the quebracho diet (69.5%). ENR was calculated from the ratio of ¹⁵N-enrichment of plasma and digesta. The ENR for the quebracho diet was 300% higher than for the control diet (6.03 vs. 1.94 g/kg dry matter intake, P < 0.001). The real N digestibility (92.2 ± 0.4%) was equal for both diets (P = 0.1030) and both tracer methods (P = 0.9730). We concluded that oral administration of [¹⁵N]leucine provides reasonable estimates of ENR in pigs fed semipurified diets with high or low content of tannins; however, one must be careful in extrapolating this conclusion to studies with other protein sources or feeding frequencies.

KEY WORDS: • ¹⁵N-isotope dilution technique • oral label administration • first-pass uptake • endogenous N • quebracho tannin