Effect of particle size on performance. 1. Corn

The effect of diets prepared with corn ground in a hammer mill and sieved to obtain "coarse", "medium", and "fine" particle size fractions, on broiler performance from hatch to 7 d and from 7 to 21 d of age was studied. Five diets differing in geometric mean diameter (GMD) or geometric standard deviation (GSD) were assayed. The best performance in both age groups studied was obtained with the diet prepared from medium corn. In this diet the GMD was .769 mm, quite similar to those of two other diets (GMD .793 and .706 obtained by mixing the original corn with 18 or 36% "fine" fraction) with which lower performance was obtained. The uniformity of the particle size (described by the GSD) also had a positive effect on performance. The improved performance obtained with the diet containing the medium corn particle size could be partly attributed to lower GSD, which was 1.63 vs about 2.00 in the other diets.