Particle size of cereal grains is an important consideration as it can influence nutrient digestibility and thus growth performance. For every 100 micron reduction in particle size, down to 300 microns, a ~1% improvement in F/G can be observed due to the improved nutrient digestibility. Reducing the particle size of corn and other ingredients to approximately 550 to 600 microns (when measured with a flow agent) improves the energy digestibility but does not influence the digestibility of phosphorous or amino acids (Mavromichalis et al., 2000; Rojas and Stein, 2015; Saqui-Salces et al., 2017). Diet form should also be considered because reducing grain particle size below 500 microns in mash diets can negatively affect feed flowability (Gebhardt et al., 2018). Reducing particle size also can potentially increase incidence of gastric ulcers leading to decreased growth performance and increased mortality (Ayles et al., 1996; Millet et al., 2012).
In summary, reducing particle size improves F/G due to an improvement in energy digestibility and the recommended particle size of finishing diets is 500 - 600 microns.