Response of nutrient digestibilities to feeding diets with low and high levels of soybean trypsin inhibitors in growing pigs

Studies were carried out to determine the effect of dietary soybean trypsin inhibitor (SBTI) content on nutrient and energy digestibilities in growing pigs. Six barrows, average initial body weight (BW) 47.8 +/- 4.0 kg, were fitted with a simple T-cannula at the distal ileum and fed two diets according to a crossover design. Two maize starch-based diets were formulated to contain 200 g crude protein (CP) kg(-1) from either Nutrisoy (a food-grade defatted soy flour) or autoclaved Nutrisoy. The contents of SBTI in the Nutrisoy and autoclaved Nutrisoy diets were 13.4 and 3.0 g kg(-1), respectively. The experiment consisted of two periods of 12 days each. The average BW at the start of the first and second experimental periods were 53.3 +/- 3.7 and 61.0 +/- 5.1 kg, respectively. The average BW at the conclusion of the experiment was 71.8 +/- 7.6 kg. The ileal digestibilities of dry matter (DM), organic (OM), energy, CP and all amino acids measured were higher (P < 0.01) in pigs fed the autoclaved Nutrisoy diet. The energy digestibility increased from 66.0 to 77.9%, and the CP digestibility increased from 37.4 to 77.1%. The increases in ileal digestibilities of the indispensable amino acids ranged from 27.0 (methionine) to 49.2 (leucine) percentage units. The increases in ileal digestibilities of the dispensable amino acids ranged from 30.2 (aspartic acid) to 50.8 (tyrosine) percentage units. The faecal digestibilities of all criteria measured were also higher (P < 0.01) in pigs fed the autoclaved Nutrisoy diet. Furthermore, there was a greater (P < 0.01) net disappearance (g kg(-1) DM intake) of DM, OM, CP, energy and all amino acids in the large intestine of pigs fed the Nutrisoy diet. In conclusion, feeding diets containing high levels of SBTI decreased both ileal and faecal digestibilities of all criteria measured. The formation of SBTI-enzyme complexes is likely to be responsible for the reduction in protein digestion and amino acid absorption. (C) 1998 SCI.