The apparent ileal digestibility (AID) of amino acids by growing pigs is increased if oil is added to the diet (Li and Sauer, 1994; Albin et al., 2001). Standardized ileal digestibility values (SID) for crude protein and amino acids take into account the amino acid contributions of endogenous origins, and values for SID are more accurate estimates of the digestibility of amino acids in a feed ingredient compared with values for AID (Stein et al., 2007). However, there is limited information about the effect of dietary oil on the SID of amino acids in soybean products fed to pigs. It has been suggested (NRC, 1998) that the digestibility of amino acids in full-fat soybeans (FFSB) is less than in soybean meal (SBM) and soy protein concentrate (SPC). This is surprising because full-fat soybeans contain more oil than SBM and SPC (Cromwell, 2000; Zarkadas and Wiseman, 2005), and it would, therefore, be expected that the digestibility of amino acids in FFSB is greater than in defatted soybean products. Because increased protein concentration in soybeans is often accompanied by a reduced concentration of oil (Yaklich, 2001), the digestibility of amino acids in high-protein soybean varieties may be different from the digestibility in conventional varieties. The objective of this experiment was to measure the effect of oil addition to SBM and SPC on AID and SID of crude protein and amino acids by growing pigs and to compare these values to the AID and SID for crude protein and amino acids in FFSB. The second objective was to compare the digestibility of amino acids and the concentration of digestible amino acids in a new high-protein variety of FFSB (FFSB-HP) to values obtained in conventional sources of FFSB (FFSB-CV), SBM, and SPC. Four diets were prepared using each soybean product as the sole source of crude protein and amino acids in 1 diet. Two additional diets were formulated by adding soybean oil (7.55 and 7.35%, respectively) to the diets containing SBM and SPC. A nitrogen-free diet was also used to measure basal endogenous losses of crude protein and amino acids. The 2 sources of FFSB were extruded at 150°C before being used in the experiment. Seven growing barrows (initial BW = 26.2 kg) were prepared with a T-cannula in the distal ileum and allotted to a 7 × 7 Latin square design. Ileal digesta were collected from the pigs on day 6 and 7 of each period. All digesta samples were lyophilized and analyzed for DM, crude protein, amino acids, and chromium, and values for AID and SID of crude protein and amino acids were calculated. The addition of oil improved (P < 0.05) the SID of most indispensable amino acids in SBM and SPC. The SID for 6 of the indispensable amino acids in FFSB-HP were greater than in FFSB-CV, and the SID for all indispensable amino acids except Met was greater in FFSB-HP than in SBM. However, the SID for most amino acids in FFSB-HP was similar to SBM with oil and SPC, but these values were lower than in SPC with oil. In conclusion, the addition of oil improved the SID of most amino acids in SBM and SPC fed to growing pigs, and the SID of amino acids in FFSB-HP were greater than in SBM and similar to the SID of amino acids in SBM with oil and in SPC.

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