Results and Discussion
Statistical Analysis and Findings
Samples were initially submitted in duplicate or triplicate, designed to represent ground corn from more than a single batch of feed. Results showed no effect of replicate, indicating that the performance of the individual grinder (average micron size) did not change from batch to batch, so the average values of the samples submitted were used in the statistical analyses. Using linear statistical models, we analyzed the effect of type of mill (hammer vs. roller) and type of operation (producer vs. elevator) on the average micron size of the samples submitted (Table 3). Our findings indicated that in the sample of grinders tested, ham mer and roller mills were statistically different in their ability to grind corn. The roller mills tested had an average micron size improvement of 200 microns over the hammer mill and were less variable than roller mills tested. The micron size of corn ground at elevators was also found to be significantly smaller than corn processed on the farm. This indicates elevators are doing a better job of grinding than that of producers on the farm.
Results of a sub-set analysis on Hammer mills (Table 4), adjusted for the effect of screen size, showed that corn ground at an elevator was much closer to the indicated target of 700 micron than corn ground through a hammer mill on the farm. Screen size was a very important factor in the ability of the hammer mill to achieve a target corn micron size of 700 (Table 5). As the size of the screen increased, we saw a linear increase in the final micron size, with screens less than 3/16th inch performing best with a target of 700 microns in the ground corn. As indicated in Table 1, variation in micron sizes is expected for a given screen size, but what is important is that for the hammer mills tested, increasing the size of the screen will result in higher micron sizes. Newer, industrialized and built hammer mills can process corn to an appropriate micron size using larger screen sizes (> ½ inch), but in typical on-farm situations, larger screen sizes contribute to larger than desired micron sizes.
The average number of pigs fed per year for the operations monitored was 9,906 pigs with a range from 250 up to 80,000 pigs fed per year. To evaluate the impact of number of hogs fed on micron size achieved, producers were classified into the following categories: < 2000 head, 2000 to 5000 head, 5000 to 10,000 head and >10000 head, with 23, 13, 9 and 14 operations represented, respectively (Table 6). Results indicated that across hammer and roller mills, the size of the farm operation affected the micron size achieved. Smaller farms (<2000) achieved higher average micron sizes than the other 3 categories, with the larger (5000 to 10,000) achieving micron sizes closest to the optimal 700 microns. This appears to be one of the contributing factors to greater efficiencies in larger operations, and one that smaller farms should not accept. With proper attention to detail and proper equipment, any size of operation can grind feed properly.