[Endogenous N-secretion in the small intestine of pigs]

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

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.

Comparison of the isotope dilution method for determination of the ileal endogenous amino acid losses with labelled diet and labelled pigs

The aims of the present study were first to compare the amino acid dilution method performed using labelled animals with that using labelled diets, and second to determine real digestibilities and total ileal endogenous losses of N and amino acids. Two diets containing pea cultivars (Solara and Amino) and a protein-free diet were compared in a 3 × 3 Latin-square experiment. The three pigs were each prepared with an ileo-rectal anastomosis and were continuously infused with [1-13C]leucine. For each cultivar,15N-labelled and unlabelled diets were formulated. The real digestibility and endogenous losses of leucine were higher when obtained by labelling the pig than by labelling the foodstuff. This was due either to the inadequate estimation of the endogenous protein enrichment in the first case or to the importance of dietary N recycling in the second case. However, in both cases the ileal endogenous losses of N and amino acids were higher than the basal losses determined with the protein-free diet. There were significant differences between the two pea cultivars in terms of phenylalanine and leucine when measured with labelled diets. It is suggested that, although ileal endogenous losses may be underestimated, using labelled feedstuffs is of great interest due to the direct estimation of the individual amounts of amino acids.

[Use of 51-Cr2O3 and TiO2 as markers for the determination of passage rate and protein digestibility in rats]

In a tripartite experiment with five rats each the suitability of 51Cr2O3 and TiO2 as markers was tested for estimating the transit time and passage rate as well as the total protein digestibility and the proportion of endogenous nitrogen in the small intestine with very small samples. Both markers are suited for these tests because of their simple analysis, their high recovery rate (94...105% for 51Cr2O3; 98...105% for TiO2) and their quantitative excretion in faeces within 3 days. Depending on the level of crude fibre (5.1 resp. 9.4% of DM) the transit time was found to be 7...8 h for a commercial breeding feed and 5...6 h for this commercial feed +15% straw meal. After the application of a single doses, the marker excretion of 50% appeared within 10 +/- 1 h resp. 8 +/- 1 h, and after the 12th hour there were no significant differences at all. The apparent N-digestibilities estimated by the conventional or the 51Cr2O3 resp. TiO2 indicator method did not show any differences. The proportion of endogenous nitrogen at the end of the small intestine calculated on the basis of the indicator dilution method was 83 +/- 11% for 51Cr2O3 and 83 +/- 12% for TiO2.

[Determination of endogenous nitrogen in feces using the isotope technic]

A ration consisting of wheat gluten and N-free components was supplemented with L-lysine and L-leucine and fed to two groups of growing Wistar rats. Group 1 received 15N Lys and unlabelled Leu, group 2 received unlabelled Lys and 15N Leu in order to study the influence of the utilization of the 15N marker on the labelling quota of faeces and urine as well as various fractions of the body. The good utilization of Lys in group 1 results in a higher 15N excess in faeces and a reduced 15N abundance in urine in comparison to group 2 with a lower utilization of 15N Leu. The results show that the 15N abundance in urine is unsuitable as an indicator of the 15N labelling quota of endogenous metabolic faecal nitrogen.

[Nitrogen and amino acid resorption in the small intestine of growing swine. 1. Animal study method, nitrogen content and amino acid composition of the small intestine chyme by administration of various proteins]

The amount of endogenous N in the chyme at the end of the small intestine and the amino acid composition of the ileum chyme were ascertained with growing pigs with ileorectostomy after feeding qualitatively differentiated protein sources. In dependence on the protein used, distinct differences turned out for some amino acids with regard to their content in the ileum chyme. Bacteriologic and histologic investigations subsequent to the dissection of the test animals showed that - in comparison to the control animals-the functions of the small intestine remained the same during the time of the experiment. The experiment method described appears to be suitable for absorption investigations up to the end of the small intestine of growing pigs.

[Absorption and use of differently structured protein isolates by rats]

Differently structured isolated proteins with the same amino acid composition were tested with growing albino rats in an N-balance and absorption experiment. The following items were tested: --isolated horse bean protein --hydrolysed isolated horse bean protein with an amino acid supplement to make up for losses due to hydrolysis --horse bean protein-casein (1:1) fibres --isolated horse bean protein with an amino acid supplement to achieve the same amino acid concentrations as in the horse bean protein-casein fibres. The lowest digestibility and utilisation values were ascertained for the hydrolysed protein. Endogenous N-excretion calculated according to the isotope dilution method was higher than for intact proteins, the transport of the chyme in the digestive tract and the true absorption of N in the small intestine had significantly diminished. In comparison with horse bean protein supplemented with amino acids, the horse bean protein-casein fibres showed decreased protein utilisation and increased endogenous N-excretion. Independent of the protein fed and of the time after feeding a relatively constant endogenous N-quota of approximately 70% could be ascertained in the chyme in the small intestine. In contrast to this, the relation between exogenous and endogenous N determined from the contents of the large intestine proved to be dependent on the intermediary utilisation of the protein fed.