Effect of particle size and heat treatment of soybean meal on standardized ileal digestibility of amino acids in growing pigs.

A study with growing barrows was conducted to evaluate of variations in particle size and degree of heat treatment during processing on standardized ileal digestibility (SID) of AA in soybean (Glycine max) meal (SBM). A commercial SBM batch was visually identified as being overtoasted due to its brownish color and was separated into small and large particles using a 1-mm sieve. In addition, 3 SBM were produced from 1 batch of soybean and exposed to different processing conditions (temperature and direct steam contact) referred to as mild (105°C; 34 min), medium (115°C; 45 min), and strong (139°C; 7 min). In total, 5 SBM-corn (Zea mays) starch-based diets were formulated to contain SBM as the sole protein source. This experiment was conducted according to a 6 × 6 Latin square design using 6 barrows (23 kg initial BW) fitted with a T-cannula at the distal ileum. With increasing particle size, SID of His and some dispensable AA increased (P < 0.05). Lower SID values in small compared to large SBM particles indicate more pronounced heat damage possibly due to increased surface area. The SID of CP and AA was lowest in the mild, intermediate in the strong, and highest in the medium toasted SBM (P < 0.001). These differences in SID are reflected in varying contents of trypsin inhibitors, Lys, reactive Lys, and NDF. In conclusion, both differences in particles size and variations in thermal processing conditions of SBM may affect SID of CP and AA.