An experiment was conducted to determine the apparent (AID) and standardized ileal digestibility (SID) of crude protein and amino acids in weanling pigs of four soybean products, fish meal, and casein. The four soybean products were conventional dehulled soybean meal (SBM), soy protein isolate (SPI), fermented soybean meal (FSBM), and enzyme-treated soybean meal (ESBM). Seven weanling barrows (initial BW of about 10.9 kg) were individually fitted with a T-cannula in the distal ileum. The barrows were allotted to a 7 x 7 Latin square design with 7 diets and 7-day periods. Six cornstarch-based diets were prepared using each of the protein sources as the sole source of crude protein and amino acids. An N-free diet was used to measure basal endogenous losses of crude protein and amino acids.

Results showed that except for Lysine, the AID and SID of amino acids in FSBM were not different from SBM, and with a few exceptions, the AID and SID of most amino acids in SBM, FSBM, and ESBM were not different from each other and from the AID and SID of the amino acids in fish meal. Likewise, the AID and SID of amino acids in ESBM and SPI were not different, but the AID and SID of most amino acids in SPI were greater (P < 0.05) than in SBM and FSBM. The AID and SID of most amino acids in SPI were not different from the AID and SID of amino acids in casein. The research group concluded that the fermented soybean meal and the enzyme-treated soybean meal had similar ileal digestibilities of most amino acids compared to conventional dehulled soybean meal, whereas, soy protein isolate had the highest ileal digestibilities of amino acids among the four soybean products.