Ileal recovery of endogenous amino acids in pigs

Ileal recovery of endogenous amino acids is important for determining balanced homeostasis of protein metabolism in pigs and the true digestibility of dietary protein. In this context, the ileal recoveries of endogenous amino acids were determined in growing pigs fed guanidinated Nutrisoy protein test meals with low and high concentration of soybean trypsin inhibitors (SBTI) using the homoarginine ratio method. Although, there were some differences in the amino acid composition between guanidinated and unguanidinated Nutrisoy the homoarginine ratio method was an effective approach to determine qualitative increases in endogenous recoveries of amino acids when the protein test meals had a higher concentration of SBTI. The in vitro incubation of soybean meal with a commercial protease increased protein solubility and decreased the content of SBTI. However, neither apparent or true ilea[ amino acid digestibilities were improved in newly weaned piglets fed protease-treated soybean meal. Recoveries of endogenous branched-chain and aromatic amino acids were higher on d 6 to 7 than d 15 to 16 after weaning, suggesting dietary change- and/or age-dependent adaptive increases in the secretions of pepsin and pancreatic proteases. In contrast, bacterial contributions to total and endogenous recoveries of nitrogen and amino acids in Ileal digesta of the piglets increased with time after weaning. In this respect, the enterobacteriaceae act as a nitrogen-sink by assimilating available dietary and endogenous amino acids, thereby, making them unavailable for absorption by the piglets. Total exchange of amino acids across the portal vein-drained tissue of pigs fed a cornstarch-based wheat gluten diet was 55.8 and 130.2 mmol/h for the plasma free amino acid and plasma peptide pools, respectively. The corresponding numerical estimate of 77.6 mmol/h for red blood cells was statistically not significant ( P >0.1) because of large standard errors from accumulated analytical variation. Similar amino acid profiles of wheat gluten and the plasma peptide pool indicate that a substantial proportion of dietary amino acids were exchanged into and transported by the portal vein blood in the form of plasma peptides. The high content of serine and threonine (intestinal mucus) and glutamate, aspartate and the branched-chain amino acids (pancreatic secretions) suggests that some plasma peptides were of endogenous origin. The exchange of amino acid across the portal vein-drained tissue of pigs is a dynamic process that involves the plasma free amino acid and plasma peptide pools and probably red blood cells.