Nutritional evaluation of soybean meals varying in particle size

The objective of this study was to evaluate the effect of varying soybean meal (SBM) particle sizes on nutritional value of the SBM. Seven samples of dehulled solvent-extracted SBM from the same batch were ground to varying mean particles of <386, 466, 809, 1,174, 1,577, 2,026, and 2,321 μm. Two precision-fed rooster assays (crop intubation with 25 g of SBM followed by 48 h total excreta collection) were performed to determine TME_n and standardized amino acid (AA) digestibility. There were no significant differences for TME_n among SBM samples, and there was also no consistent significant effect of particle size on standardized AA digestibility. In addition to the 2 precision-fed rooster assays, a 21 d broiler chick trial was conducted using corn-SBM based diets using 4 diets that differed only in the mean particle size of SBM (466, 809, 1,174, or 1,577 μm), being fed from 2 to 23 d of age. Chicks fed diets containing 809 or 1,174 μm SBM had increased (P < 0.05) weight gain compared with chicks fed the diet containing 466 μm SBM, and chicks fed diets containing 1,174 or 1,577 μm SBM had increased (P < 0.05) feed efficiency compared with chicks fed the diet containing 466 μm SBM. The diet containing 466 μm SBM yielded the highest (P < 0.05) AME_n and total tract P retention. Ileal P digestibility and standardized AA digestibilities did not differ among treatments. Relative gizzard weight (percent of body weight) was increased (P < 0.05) by the 2 largest SBM particle sizes. The results from these 3 experiments showed that increasing SBM particle size may be beneficial to broiler growth performance and may increase gizzard size but had no consistent significant effect on ME, AA digestibility, or P digestibility/retention.