Influence of feed particle size on the performance, energy utilization, digestive tract development, and digesta parameters of broiler starters fed wheat- and corn-based diets.

The influence of particle size and grain type on the performance, AME(n), and on gross morphological and histological parameters of the various segments of the digestive tract of broilers fed wheat- or corn-based diets was investigated. The experimental design was a 2 x 2 factorial arrangement of treatments evaluating 2 particle sizes (fine and coarse) and 2 grain types (wheat and corn). The 2 particle sizes were achieved by grinding the whole grains in a hammer mill to pass through 1-mm and 7-mm screen sizes. Broiler starter diets, based on wheat- or corn-soybean meal, were formulated, pelleted, and each diet was offered to 6 cages of 8 male broilers each from d 1 to 21 posthatching. The results showed that the differences in particle size distribution still existed between diets after pelleting especially in the proportion of coarse particles (1 mm and over). In corn-based diets, coarse grinding improved (P = 0.06) weight gains compared with fine grinding, but this particle size effect was not observed in wheat-based diets. In both diets, coarse grinding lowered (P < 0.001) feed per gain of broilers compared with fine grinding. In wheat-based diets, coarse grinding improved (P = 0.06) AME(n) compared with fine grinding. Heavier (P < 0.05) gizzard weights were observed in birds fed the coarse corn-based diet, but particle size had no effect on the gizzard size in birds fed wheat-based diets. Villus height, crypt depth, and epithelial thickness in the duodenum were unaffected (P > 0.05) by particle size and grain type. Overall, the present results showed that the effect of feed particle size varies depending on grain type.