Protein digestion in weanling pigs: effect of dietary protein source

The digestion and absorption of dietary protein was measured in weanling pigs (5 wk of age). Diets containing corn and either dried skim milk (DSM), soybean meal (SBM) or corn gluten meal (CGM) were fed for 7 d, and the contents of the stomach and six segments of the small intestine were collected. Nitrogen digestibility increased linearly from the proximal duodenum to the distal ileum, and was highest for DSM, intermediate for SBM and lowest for CGM diets at the distal ileum. The content of free amino acids in digesta increased 8-fold (SBM and CGM) to 12-fold (DSM) between the stomach and the proximal duodenum and reached a maximum concentration in the distal jejunum. Digestion of DSM was more proximal than was that of SBM. Although there was some accumulation of small peptides in the duodenum with a subsequent decrease in the jejunum, the molecular weight profiles of the soluble proteins were relatively constant throughout the small intestine. Protein solubility and the rate of proteolysis in the stomach and upper small intestine were the primary factors that limited the digestion of SBM and CGM.