Nitrogen metabolism in gastrointestinal tissue of the pig.

The protein content of the gastrointestinal tract is not more than 7 % of whole-body protein, while the amount of protein synthesized daily exceeds 20% of whole-body protein synthesis. Considering this active protein metabolism in the gastrointestinal tract as well as the role of the gastrointestinal tract in digestion and absorption, we have investigated fluxes of N and amino acids (AA) in relation to diet composition. This work was carried out within the framework of looking at possibilities of further increasing the efficiency of N utilization in growing pigs, which has both economic and environmental implications. The present article reviews N metabolism in the gastrointestinal tract of the pig and fluxes of N and AA after digestion and absorption by the gastrointestinal tract in relation to diet composition. AA and peptide transport by the intestine has been reviewed recently (Daniel et al. 1994; Munck & Munck, 1994; Mailliard et al. 1995) and is not considered here.