Nitrogen utilization in pigs as affected by dietary induced losses of ileal endogenous nitrogen

<p>The results of this thesis showed that various protein sources (feedstuffs) have different values for apparent and true ileal digestibilities of protein and thus also of ileal endogenous nitrogen losses (ENL; determined with the <sup>15</sup> N-isotope dilution technique). It was initially hypothesized that increased ENL may induce an increased recycling of endogenous proteins. As a result of the latter, increased nitrogen (N) losses may occur in urine because of inefficiency of metabolic processes. Furthermore, the increased ENL may lead to a decreased utilization of small intestinal dietary N for retention in pigs. In this context, when using feedstuffs that led to a distinctly different ENL, the results of N balance in pigs were in agreement with the starting hypothesis. Further, it was found that feedstuffs with protease inhibitor-related ENL reduced the dietary N utilization and increased urinary N loss. For feedstuffs with various ENL related to fibre per se, the urinary N loss and dietary N utilization for retention did not differ significantly. It means that ENL- and N metabolism differ depending on the feed factors to which the ENL are related. These results indicated that (1) total secretion of endogenous N may not be related to the level of ENL, and (2) the reabsorption ratio of the secreted endogenous N may vary for different feedstuffs. Based on that, the starting hypothesis was modified to: mainly, the magnitude of ENL (i.e., first- limiting amino acids) determines the inefficiency of dietary N utilization rather than the magnitude of total recycled endogenous N. Thus, increased urinary N losses may depend on the extent of amino acid oxidation resulting from the amino acid imbalance caused by the ENL In the particular experimental conditions (restricted protein/AA intake), extra supplementation with crystalline amino acids of a diet with high protease inhibitor-related ENL improved the utilization of the dietary N and decreased extra urinary N loss. It seems, therefore, that extra amino acid addition can compensate for the ENL by improving the profile of amino acids available for endogenous protein re- synthesis. As a result, the remaining dietary amino acids are in a better balance for the body protein retention. Further results showed that the total amounts of endogenous N secretions were approximately similar for different dietary factors that induce the ENL Therefore, the magnitude of the ENL rather than the magnitude of total secreted and reabsorbed endogenous N mainly determines the efficiency of dietary N utilization and extra urinary N loss. These results were in agreement with the adjusted hypothesis. Supplementation with extra amino acids may decrease environmental N losses, caused by increased ENL and increase the efficiency of dietary N utilization in pig production