Effect of Dietary Raw Soybean and Soybean Trypsin Inhibitor on Trypsin and Chymotrypsin Activities in the Pancreas and in Small Intestinal Juice of Growing Swine

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Abstract
Sixty-eight growing gilts with a 12 kg average initial weight were used in seven trials to study the effect of dietary raw soybean (Harosoy) and SBTI (Kunitz soybean trypsin inhibitor) on pancreatic and small intestinal trypsin and chymotrypsin activities. A solvent-extracted, heated soybean meal (SBM) was used as the control. The raw soybean diet, whether ad libitum fed or pair-fed, caused reduced growth. Both a single-meal and continuous feeding of the raw soybean diet caused a decrease in the pancreatic trypsin and chymotrypsin activities. In contrast to the rat and the chick, the pancreas of the pigs did not enlarge subsequent to consumption of the raw soybean or SBTI diets. Raw soybean feeding also resulted in an inhibition of the intestinal trypsin and chymotrypsin activities. This inhibiting effect was greater than that of the SBTI, especially the chymotrypsin-inhibiting effect. This suggested that soybean constituents other than the SBTI, such as the Bowman-Birk inhibitor, caused inhibition. In the pig the inhibition of the intestinal proteolysis may be a major cause of reduced growth when raw soybean is fed.