N.D. Fastinger and D.C. Mahan1
The Ohio State University Department of Animal Sciences
Abstract
A study evaluated the effect of soybean meal (SBM) particle size reduction on subsequent amino acid ileal digestibility. Soybean meal was processed through a hammer mill to achieve average particle sizes of approximately 900, 600, 300, and 150-microns. A low-protein (5% casein) diet was used to determine endogenous amino acid losses for calculating an adjusted low-protein digestibility. Fourteen crossbred barrows with an average body weight of 61.7 lb were surgically fitted with a T-cannula at the distal ileum. The amount of feed provided was based upon metabolic body weight (0.09 kg.75) and was increased 0.33 to 0.44 lb between each collection period. Treatment diets were fed at a constant level during each 7-day period with ileal digesta samples collected for 2 days following a 5-day adaptation period. Low-protein adjusted digestibility of amino acids was calculated using 0.5% chromic oxide as a dietary marker. Low-protein adjusted digestibility of isoleucine, methionine, phenylalanine, and valine were shown to increase linearly (P < 0.05) as particle size decreased. All amino acid digestibilities, with the exception of glutamate, increased numerically from the 900 to 600-micron treatment. These results suggest that a reduction in particle size of SBM increases the digestibility of its amino acids. The largest improvement in digestibility was obtained when the particle size was reduced from 900 to 600-microns.