Determination of ileal endogenous nitrogen losses and true ileal nitrogen digestibility during non-steady-state conditions of the ¹⁵N-isotope dilution technique

ABSTRACT

The aim was to determine ileal endogenous nitrogen losses (ENL) and true ileal N-digestibility (TD-N) under non-steady-state conditions of the ¹⁵N-isotope dilution technique (¹⁵N-IDT), using diets generating low and high ENL and compare results to those obtained under steady-state conditions. Twelve growing pigs (mean LW 22.4 kg) fitted with a post-valve T-caecum cannula were fed an enzyme-hydrolysed casein (EHC)-based diet or an EHC diet + 4% quebracho tannins (QT) and were labelled via continuous ¹⁵N-leucine i.v. infusion or twice daily oral ¹⁵N-leucine administration. Digesta were collected daily over three consecutive hours with blood plasma sampled on the four consecutive days after cessation of ¹⁵N-labelling. There was a significant effect of sampling day on the dilution factor. Endogenous N losses were significantly lower for the EHC than the EHC+QT diet (2.41 vs. 8.69 g/kg DMI), while no significant effect of sampling day was observed. The TD-N of the EHC+QT diet did not differ from the TD-N of the EHC diet (95.1 vs. 92.0%). A significant effect of sampling day was observed for TD-N with day 1 and 2, being higher than day 4. Non-steady-state conditions overestimated ENL by 25–28% as compared to 3 h collections in steady-state conditions, but the relative overestimation was similar for the EHC diet as for the EHC+QT diet. TD-N did not differ significantly compared to 12 h steady-state measurements, but comparison to 3 h steady-state measurements showed that non-steady-state conditions overestimated TD-N for the EHC+QT diet by 9%. However, on day 4 this overestimation disappeared. Using the ¹⁵N-IDT during non-steady-state conditions can provide valuable additional data on endogenous N losses and TD-N.

KEYWORDS:

• Ileal endogenous protein
• protein digestibility
• ¹⁵N-leucine
• isotope dilution
• non-steady-state
• pigs
• tannin
• antinutritional factors

Acknowledgments

We thank Marianne van Westerneng-van ‘t End for chemical analyses and the late Huug Boer and the late Henk Visser for coordination of the (isotope) analyses.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Supplementary material

Supplementary data for this article can be accessed at https://doi.org/10.1080/1745039X.2024.2322201

Additional information

Funding

This study was supported by the technology foundation STW of the Netherlands Organization for Scientific Research (NWO) under grant number [WBI.3193].