Effect of grain particle size on performance. 2. Grain texture interactions.

Diets were prepared with corn, wheat, or sorghum ground in a hammer mill and sieved to obtain coarse, medium, and fine particle size fractions. Their effect on broiler performance from hatch to 7 d and from 7 to 21 d of age was studied. The effect of particle size on the size and pH of the gastrointestinal organs was also determined. The three textures obtained for each grain were uniform in geometric mean diameter (GMD) and geometric standard deviation (GSD). Grain by texture interactions were not significant. Independent of grain source, the best performance was obtained with diets prepared from the medium texture. In these diets, the GMD of the grains varied from 1.13 to 1.23 mm and the GSD from 1.19 to 1.35. The fine fraction (GMD .57 to .67 mm) resulted in the lowest performance and that resulting from the coarse fraction (GMD 2.01 to 2.10 mm) was intermediate. At 7 and 21 d of age, gizzard weight and content were positively related to particle size. At the age of 21 d, duodenum weight and content was highest in chicks fed the fine diets. The pH of the gizzard content decreased with increasing grain particle size, whereas that of the small intestinal content increased. Some grain effects were also observed on the gastrointestinal tract. Gizzard weight was greatest in the cornfed birds. Wheat-fed chicks had the heavier intestines and contents. After overnight feed deprivation, feed consumption by 7-d-old chicks was related to the particle size during the first 2 h of refeeding, with greater intake of medium and coarse grains.