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Abstract. The uniformity of a feed mixture is determined from the coefficient of variation (CV) of ten samples in a single batch of feed. The feed industry standard is a CV of less than 10% using a single source tracer such as salt, trace minerals, or iron filings. The uniformity of mix can be affected by many factors, including mixer design, particle size of the ingredients, sample preparation, and mix time. Previous research has determined the minimum mix time to maximize the mixing efficiency, but some hypothesize that over-mixing may lead to ingredient segregation. However, there are limited data regarding the effects of extended mixing, appropriate particle size of the analytical marker, and the analytical sample preparation for maximum precision of the assay. The objectives of these experiments were to determine (1) the effects of extended mix time, (2) particle size of the marker, and (3) sample preparation of the CV in a corn-soy swine diet. Experiment 1 treatments were arranged in a 3 x 7 factorial with three salt particle sizes (fine-350 μm, medium-464 μm, and coarse-728 μm) and seven mix times (2, 3, 5, 15, 30, 45, and 60 min). Experiment 2 treatments were arranged in a 2 x 3 x 3 factorial with two sample preparations (unground and ground), three salt particle sizes (fine-350 μm, medium-464 μm, and coarse-728 μm), and three mix times (3, 30, and 60 min). There were three replicates per treatment and ten samples per replicate. Salt concentrations were determined using a Quantab chloride titrator. The results of experiment 1 indicated no interaction between mix time and salt particle size (p = 0.4366). The extended mix time did not result in segregation (p = 0.3073; 11.5%, 13.8%, 12.9%, 13.1%, 13.9%, 11.6% and 11.3% CV for 2, 3, 5, 15, 30, 45, and 60 min, respectively). Particle size of the salt significantly affected the mixture uniformity (p < 0.0001; 21.2%, 8.6%, and 7.9% CV for coarse, medium, and fine salt, respectively). The results of experiment 2 indicated no interaction of sample preparation, salt particle size, and mix time (p = 0.3823). However, there was an interaction between sample preparation and salt particle size (p = 0.0002). The difference in the % CV between unground and ground samples was significantly greater for the mixture with coarse salt (8.89%) than for mixtures with medium (2.59%) and fine (1.35%) salt. The ground treatment had a significantly lower % CV than the unground treatment (p < 0.0001; 8.7% and 13.0% for ground and unground samples, respectively). The fine and medium salt treatments had significantly lower % CV as compared to the coarse salt treatment (p < 0.0001; 7.4%, 7.7%, and 17.4% for fine, medium, and coarse, respectively). These results indicate that feed did not segregate after mixing for 1 h and that a greater number of particles per gram of the marker increased the precision of the analysis. This was likely due to an increased probability that the marker was present in greater proportionate quantities in the sample tested. However, when coarse salt is used in a manufacturing process, the samples should be ground prior to analysis.