Effect of Feed Particle Size and Mixing Time on the Mixing Efficiency of Animal Feeds

The effects of variable mixing periods (10, 15 and 20 min) on the homogeneity of a feed formulated from; barley (27), wheat (28), mustard cake (16), groundnut cake (16), rice polish (10), mineral mixture (2) and salt (1) were assessed. The feed ingredients (barley, wheat, mustard cake and groundnut cake) were ground through 2, 3, 4, 5, and 6mm sieves using a hammer mill. The coefficient of variation (CV %) for ash and salt contents, and number of maize grains per kg of feed sample was determined to asses the mixing efficiency of mixer. The particle size, modulus of uniformity, modulus of fineness and number of particles per gram significantly (P<0.05) affected by the type of grain used for grind. By sieving the barley ground through 2, 3, 4, 5, and 6mm sieves, the particle size increased (P<0.05) from 819–1772μ and the surface area of the particles decreased (P<0.05) from 67.5–36.0 cm2/g. The particle size increased (P<0.05) from 839–1591 μ, 622–952 μ and 615–944 μ and surface area decreased from 68.4–32.0, 94.9–65.1 and 92.4–64.8 cm2/g for wheat, GNC and MC, respectively, while the ingredients were ground through 2, 3, 4, 5, and 6mm hole sized sieves. The relative proportions of coarse particles increased and that of medium particles with in a sample decreased drastically for barley grains. The relative proportion of medium and fine particles decreased and that of course increased with the increase of pore size of sieves for GNC and MC. The average modulus of fineness was significantly (P<0.05) higher for wheat (5.26) followed by barley (3.86), MC (3.74) and GNC (3.29), however the differences between barley, MC and GNC were non-significant. The percent CV for ash, salt and number of maize grains decreased from 19.27 to 12.86%, 38.05 to 8.36% and 33.36 to 10.36% as the time of mixing increased from 10–20 minutes. The CV values were higher for the ingredients ground through 2 and 6mm hole sized sieves compared to 3,4 and 5mm hole sized screens for al 1 the three tracers. It may be concluded that mixing time of 20 minutes and grinding through 3,4 and 5mm hole sized screens is optimum for uniform mixing of various feed ingredients in vertical mixer.