GASTRIC PROTEIN BREAKDOWN AND PANCREATIC-ENZYME ACTIVITIES IN RESPONSE TO 2 DIFFERENT DIETARY-PROTEIN SOURCES IN NEWLY WEANED PIGS

Seventy pigs were weaned at 25 d of age and fed diets based on either skim-milk powder (SMP) or soybean protein concentrate (SOY). At 0, 3, 6, and 10 d after weaning, pigs were anesthetized, their pancreases were removed, and digesta were collected from different sections of the digestive tract. The ratio between trichloroacetic acid (TCA)-precipitable protein and total (crude) protein (pp:cp) in gastric digesta was higher with SOY feed than with SMP feed. In the jejunum, no difference was found; hence, the degree of protein breakdown in jejunal chyme did not differ between protein sources. Trypsin activities in jejunal chyme and in pancreatic tissue increased (P < .01) after weaning. Chymotrypsin activity in pancreatic tissue tended to decrease after weaning and did not reach ''weaning levels'' for at least 10 d. Pancreatic trypsin developed more rapidly than chymotrypsin after weaning. Chymotrypsin activities in jejunal digesta were higher (P < .05) for the pigs fed SMP than for those fed SOY. Protease activities in the jejunum at d 6 after weaning were clearly affected (P < .05) by feed intake after weaning. The ratio between trypsin and chymotrypsin activity in jejunal chyme was higher (P < .05) for SOY-fed pigs than for SMP-fed pigs. It was concluded that the stomach plays an important role in the digestion of milk protein and that the development of pancreatic proteases after weaning (synthesis, secretion, breakdown) depends on feed intake and on dietary protein source.