Quantitative and qualitative changes in endogenous nitrogen components along the small intestine of the calf

The aim of this study was to investigate the quantitative and qualitative changes in endogenous protein components along the calfs small intestine. A protein-free diet and three milk substitutes based on skim milk powder and differing in their protein level (100, 200 and 280 g kg(-1) respectively) were prepared. Duodenal, jejunal and heal digesta were collected through simple cannulae. The flow of non-specific endogenous amino acids (AAs) determined with the protein-free diet was 8, 13 and 12 g kg(-1) of dry matter intake in the duodenum, jejunum and ileum respectively. The flow of endogenous amino acids in digesta from calves fed diets containing protein was determined using multiple linear regression analysis. It was higher than the non-specific flow at the duodenum and jejunum owing to additional specific endogenous components. At the ileum, milk proteins were completely digested and the flow of total AAs assayed was equal to the non-specific flow. Seventy per cent of protein flowing at the jejunum was apparently reabsorbed before the terminal ileum. Endogenous protein at the duodenum resembled a theoretical mixture of proteins from saliva, gastric and pancreatic juices (140, 270 and 590 g kg(-1) respectively). Ileal protein losses corresponded to a mixture of proteins from the host and gut bacteria in a 50:50 ratio. By contrast, no theoretical mixture of reference proteins fitted the AA composition of jejunal endogenous protein. (C) 2000 Society of Chemical Industry.