Ileal Digestibility of Amino Acids in Conventional and Low-Kunitz Soybean Products Fed to Weanling Pigs*

An experiment was conducted to determine the standardized ileal digestibility (SID) of amino acids (AA) in four sources of full-fat soybeans (FFSB) and in one source of soybean meal (SBM). The FFSB had different concentrations of trypsin inhibitor units (TIU) and included two sources of conventional FFSB, and two sources of a soybean variety that was selected for a reduced concentration of the Kunitz trypsin inhibitor. The conventional FFSB was either low temperature-processed (LT-FFSB-CV; 37.7% CP, 35.4 TIU/mg) or high temperature-processed (HT-FFSB-CV; 40.5% CP, 4.4 TIU/mg). The low-Kunitz FFSB was also either low temperature-processed (LT-FFSB-LK; 36.2% CP, 23.5 TIU/mg) or high temperature-processed HT-FFSB-LK; (38.2% CP, 4.0 TIU/mg). The SBM contained 47.5% CP and 3.20 TIU/mg. Twelve weanling barrows (initial BW: 11.1±1.3 kg) were fitted with a T-cannula in the distal ileum. Pigs were allotted to a replicated 6×6 Latin square design with six diets and six periods per square. Five diets were prepared using each of the soybean sources as the only source of AA in the diet. An N-free diet was also included in the experiment to measure basal endogenous losses of AA. The two low temperature-processed FFSB had lower (p<0.05) AID and SID values for all indispensable AA than the two high temperature-processed FFSB and SBM. The SID values for all indispensible AA except Trp were greater (p<0.05) in LT-FFSB-LK than in LT-FFSB-CV, but the SID of AA in HT-FFSB-CV and HT-FFSB-LK were not different. The SID of AA in SBM were not different from the SID in HT-FFSB-CV and in HT-FFSB-LK. Results of this experiment show that a reduction of the TIU from 35.4 to 23.5 TIU/mg will improve the SID of AA, but this reduction is not sufficient to completely ameliorate the negative impact of trypsin inhibitors. Results also show that the SID of AA in high temperature-processed FFSB is similar to that in de-hulled SBM. (