1. Thirty-five pigs were fitted with single re-entrant cannulas in either the duodenum, jejunum or ileum. A further twenty-four pigs were used in a conventional digestibility trial.
2. Methods for collecting, sampling and returning digesta were developed.
3. A ‘practical-type’ diet and two purified diets were used, fed twice daily.
4. Flow and pH of digesta were measured hourly in the duodenum and jejunum, and every 6 h in the ileum.
5. In the duodenum and jejunum there were clear flow responses to feeding, while such an effect was not found in the ileum where the flow-rate was much lower and more uniform than in the former sites.
6. In the duodenum and jejunum, and within 6 h periods in the ileum, there was considerable variation in the flow-rate between different pigs within each hour but there was less variation in pH.
7. The pattern of flow in the duodenum and jejunum was similar for each of the diets but the total flow and the average pH in 24 h differed significantly between diets. There were more digesta of a lower pH from the ‘practical-type’ diet than the purified diets.
8. The pH in the duodenum was highest after feeding and decreased with increasing time after feeding. In the jejunum and ileum the pH varied over a much smaller range than in the duodenum.
9. Collections for 6 h periods appeared to be insufficiently long to predict the values obtained in 24 h collections with reasonable accuracy.