Four pelleted diets were prepared containing milk or isolated soya-bean protein (ISP) as the major protein source. The milk and ISP were given either as intact proteins or partially (0.650 hydrolyzed with papain before feeding. 2. The diets were given ad lib. to thirty-two pigs from 7-28 d of age. The pigs were slaughtered at 28 d of age. 3. Weight gains, food conversion ratios and nitrogen balances of pigs given diets containing milk protein were better than those of diets containing ISP (231 g/d, 0.80 and 11.5 g/d compared to 209 g/d, 0.88 and 9.00 g/d respectively). 4. Partial hydrolysis of proteins before feeding did not affect the performance of the pigs. 5. Apparent digestibilities of N before the ileum and in the whole tract were 0.78 and 0.94 for the pigs given the ISP diets and 0.86 and 0.97 for the pigs given the milk-protein diets. 6. Retention time of ISP diets in the whole digestive tract was 1475 min and that of the milk-protein diets was 1089 min. 7. pH of digesta in the stomach was 5.0-5.3 for all diets and increased to 6.9-7.1 in the ileum. 8. There were no differences in flows of total N and protein N to the ileum and lower digestive tract between the pigs given the intact-and hydrolyzed-protein diets. 9. Apparent absorptions of N in the stomach, duodenum and jejenum were greater in the pigs given diets containing hydrolyzed proteins than in those given diets containing the intact proteins. 10. Flows of total N and protein N to the ileum tract were greater when the pigs were given the ISP diets than when they were given the milk-protein diets. 11. Hydrolysis of proteins before feeding resulted in a reduced trypsin and chymotrypsin activity in the duodenum and pancreas. 12. Retention of dietary N in the carcass was greater in pigs given the milk-protein diets (0.79) than in those given the ISP diets (0.68).
