Effect of particle size on precaecal digestibility of amino acids from maize and soybean meal in broilers

Maize and solvent extracted soybean meal (SBM) were ground through a 2 or 3 mm screen, resulting in “fine” and “coarse” material. The mean particle sizes of fine and coarse feed were 0.62 vs. 0.96 mm (maize) and 0.63 vs. 1.01 mm (SBM). Maize or SBM of either particle size was included in experimental diets at two different levels at the expense of maize starch. Three week old broilers had free access to one of the 9 diets for a period of 7 days. Six pens of 10 broilers were allocated to each diet. Digesta was sampled from a standardised section of the terminal ileum immediately after slaughter. Precaecal digestibility of amino acids was calculated for maize and SBM by linear regression analysis, which considers the basal endogenous amino acid losses. All amino acids from coarse maize were higher digested than from fine maize, with a mean difference of 6.3%. In contrast, all amino acids from coarse SBM were less digested than from fine SBM, with a mean difference of 5.5%. It is concluded that particle size affects amino acid digestibility and that this effect is different between feed ingredients. Therefore, standardising particle size is important in routine studies on amino acid digestibility of feed ingredients.