Influence of feed particle size and feed form on the performance, energy utilization, digestive tract development, and digesta parameters of broiler starters.

This study investigated the influence of particle size and feed form on the performance, the AME(n), and the gross morphological and histological parameters of various segments of the digestive tracts of broilers fed wheat-based diets. The experimental design was a 2 x 2 factorial arrangement of treatments evaluating 2 wheat particle sizes (medium and coarse) and 2 feed forms (mash and pellet). The 2 particle sizes were achieved by grinding the whole wheat in the hammer mill to pass through 3- and 7-mm sieves. Broiler starter diets, based on wheat and soybean meal, were formulated and each diet was fed to 6 pens of 8 male broilers each from d 1 to 21 posthatching. Broiler performance was superior (P < 0.05) in birds fed pelleted diets compared with those on mash diets. Pelleting evened out the differences in particle size distribution between treatments and, as a result, wheat particle size had no effects (P > 0.05) on the performance of broilers fed pelleted diets. In mash diets, coarse grinding of wheat improved (P < 0.05) weight gain and feed:gain compared with medium grinding. Pelleting had a negative effect (P < 0.05) on AME(n). The improvement in bird performance with pelleting was accompanied by a decrease in the relative length of all components of the digestive tract. Conversely, the extent of the mucosal layer was greater (P < 0.05) in both the duodenum and jejunum of birds fed pelleted feeds. Feed form influenced (P < 0.05) the particle size of duodenal digesta, whereas particle size had no effect (P > 0.05). Overall, the current results showed that feed form had a greater influence on the different measured parameters than did particle size.