The amino acid concentrations of cornstarch-based guanidinated unprocessed (UGM) and autoclaved (AGM) Nutrisoy (defatted soy flour) protein test meals were compared with the respective unguanidinated Nutrisoy diets. Endogenous ileal recoveries and true digestibilities of amino acids were determined in six growing pigs, fitted with a simple T-cannula at the distal ileum, fed the guanidinated protein test meals. The UGM and AGM contained 13.4 (high) and 3.0 (low) g/kg dry matter of soybean trypsin inhibitors (SBTI), respectively. The experiment was a two-period cross-over design with each period lasting 15 d. On d 14 of each period, the pigs were fed the guanidinated test meals followed by 24 h continuous collection of digesta. Concentrations of crude protein and most of the amino acids in the test meals were higher than in the respective diets. Apparent ileal amino acid digestibilities of the test meals did not differ (P > 0.05) from reported values for the respective diets and were higher (P < 0.05) by 22.7 (cysteine) to 61.3 (tyrosine) percentage units for AGM compared with UGM. The ileal recoveries of endogenous amino acids in AGM-fed pigs were lower (P < 0.05) than UGM-fed pigs. Values ranged from -0.10 (arginine) to 0.64 (aspartate + asparagine) and from 0.84 (histidine) to 2.61 (tyrosine) g/kg dry matter intake for AGM- and UGM-fed pigs, respectively. True ileal amino acid digestibilities for AGM were higher (P < 0.05) than UGM with differences ranging from 12.7 (tyrosine) to 38.3 (leucine) percentage units. In conclusion, ileal recoveries of endogenous amino acids were increased in pigs fed guanidinated protein test meals with the higher concentration of SBTI.

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: Studies were carried out to determine the e †ect of dietary soybean trypsin inhibitor (SBTI) content on nutrient and energy digestibilities in growing pigs. Six barrows, average initial body weight (BW) 47É8^4É0 kg, were Ðtted 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 Ñour) or autoclaved Nutrisoy. The contents of SBTI in the Nutrisoy and autoclaved Nutrisoy diets were 13É4 and 3É0 g kg~1, respectively. The experiment consisted of two periods of 12 days each. The average BW at the start of the Ðrst and second experimental periods were 53É3^3É7 and 61É0^5É1 kg, respectively. The average BW at the conclusion of the experiment was 71É8^7É6 kg. The ileal digestibilities of dry matter (DM), organic (OM), energy, CP and all amino acids measured were higher (P \ 0É01) in pigs fed the autoclaved Nutrisoy diet. The energy digestibility increased from 66É0 to 77É9%, and the CP digestibility increased from 37É4 to 77É1%. The increases in ileal digestibilities of the indispensable amino acids ranged from 27É0 (methionine) to 49É2 (leucine) percentage units. The increases in ileal digestibilities of the dispensable amino acids ranged from 30É2 (aspartic acid) to 50É8 (tyrosine) percentage units. The faecal digestibilities of all criteria measured were also higher (P \ 0É01) in pigs fed the autoclaved Nutrisoy diet. Furthermore, there was a greater (P \ 0É01) 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. ( 1998 SCI.