1. Three pigs prepared with re-entrant cannulae in the proximal duodenum and terminal ileum were used to study flow rate of nitrogen, and digestion and absorption of dry matter, nitrogen, gross energy and starch. The pigs were given a semi-purified diet, a hard wheat diet and a soft wheat diet. These were approximately isonitrogenous.
2. Nitrogen content of insoluble dry matter of duodenal digesta was much higher on the semi-purified diet than on the wheat-based diets.
3. Apparent digestibilities of dry matter, energy and nitrogen in the small intestine were in the order semi-purified diet > hard wheat > soft wheat although differences were not statistically significant. Similar results were obtained for total digestibility of these components.
4. Absorption of most amino acids from the small intestine was higher for casein in the semi-purified diet than for wheat protein. Significantly more lysine, arginine, isoleucine and tyrosine were absorbed from hard than from soft wheat.
5. With all diets there was almost complete digestion of starch in the small intestine.
6. There was little digestion of nutrients in the large intestine, and thus digestibilities calculated from faecal analyses showed similar trends to those calculated from analyses of digesta from the terminal ileum. Most values compared favourably with those reported elsewhere for digestibilities of amino acids in wheat.
7. It was concluded that casein was superior to the wheat proteins but that protein of hard wheat was of better quality than that of soft wheat when evaluated by ileal recovery of animo acids, due largely to a greater absorption of lysine.