Likewise, the bulk density of grain and vitamin and trace mineral premixes varies. Unless the mixing equipment is calibrated periodically, variations in the nutrient content of diets could be large and affect performance and profits. Check the bulk density of a new supply of any ingredient if you mix feed by volume. Changes in bulk density are easily detected by keeping a record of the exact weight of each ingredient required to fill the container level full. A good rule of thumb is to recalibrate the mixing equipment for all diets containing an ingredient in which the bulk density changes more than 5 percent.
Some producers use results from a laboratory feed test to calibrate their mixing equipment.
A vertical mixer is essentially a holding bin with a vertical screw in the center. Because the screw can move only a fraction of the total amount of feed in the mixer at one time, about 15 minutes is necessary to adequately mix the ingredients after the last ingredient is added to the mixer. Feed ingredient segregation will not occur even if mixing times exceed 15 minutes. Horizontal and drum mixers should run for 5 to 10 minutes after addition of the last ingredient. Wear on the screw, ribbons, and paddles of mixers significantly reduces mixing action, and increases the mixing time required.