Same Old Grind? Maybe Not

How you grind feed in your operation is important due to its impact on nutrient digestibility, which directly affects feed cost per pig. But the factors involved in determining benefits are many and varied, as shown by two recent research studies.

Researchers at Kansas State University report that a 2-high roller mill or hammer mill has been the standards to grind corn but it is difficult to achieve high throughput and a consistent particle size below 600 microns. As a result, many U.S. feed mills have installed 3-high roller mills to more consistently achieve target particle sizes. A limited number of mills use 4-high roller mils to achieve even finer and more consistent particle size targets, but the KSU researchers say there is limited evidence that 3- or 4-high roller mills will improve income over feed costs (IOFC). They performed a study to evaluate the effects of different roller-mill configurations on pig performance and IFOC.

The study compared 2-high (approx. 667 microns); 3-high (approx. 536 microns); 4-high fine (approx. 350 microns; and 4-high coarse (approx. 478 microns). All corn was processed in a commercial feed mill. In the first two experiments, nursery pigs were used and in the third, finishing pigs were used.

In Experiment 1, the researchers report there were no differences in average daily gain (ADG), average daily feed intake (ADFI), feed/gain ratio or IFOC. In Experiment 2, nursery pigs preferred a coarser particle size (667 vs 350 and 478 vs 350). In Experiment 3 with finishing pigs, feed in the 2-high configuration had the best ADG and ADFI while the finer ground particles produced the lowest ADG and ADFI. Feed cost per lb. of gain was lowest for 4-high coarse feed and revenue per pig was greatest for the 2-high and 4-high coarse configurations.

Different Results in Illinois
The results of research at the University of Illinois indicate that it is possible to reduce feed costs if corn is ground to a finer particle size in swine diets. Researchers there found smaller particle size allows pigs to derive more energy from the corn, which means producers can reduce the amount of fat added to diets without affecting growth performance or carcass characteristics.

"When corn is ground to smaller particle sizes, pigs can derive more energy from it because the increase in surface area means that digestive enzymes have more access to the nutrients in corn, which results in increased digestibility of starch," said Hans Stein, UI professor of animal sciences. "Therefore, you can reduce the amount of fat added to the diets without a loss of metabolizable energy if you use more finely ground corn. In this study, we tested the hypothesis that added fat can be removed from diets containing finely ground corn without impacting growth performance and carcass characteristics of the pigs."

The researchers fed grow-finish pigs diets containing corn ground to 865, 677, 485, and 339 microns. Diets were formulated to contain the same amount of metabolizable energy by varying the amount of added fat. The diets using the most coarsely ground corn contained 3.60 to 3.87 percent fat, whereas the diets using the most finely ground corn contained 2 percent fat.

The carcass characteristics of all the pigs were very similar. Backfat depth, hot carcass weight, loin eye area, pH of loin eye area, and fat-free lean percentage were not affected by particle size. However, dressing percentage increased, and empty intestinal weight decreased as particle size decreased.

Growth performance was also unaffected by corn particle size. The pigs' final body weight, overall ADFI, and overall ADG were not different among treatments.

These results indicate that it is possible for producers to reduce feed costs if corn is ground to a finer particle size, but the Kansas State study produced different findings. More research is necessary to determine the overall impact of smaller corn particle size.



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