Over an 18-month period, Kansas State University (KSU) researchers collected 674 one-half pound feed samples from producers. Analysis of the samples found that 65% were in the recommended 600 to 800 micron range for particle size. The optimum range is 650 to 750 microns. (See Figure 1.)

This data shows an improvement over particle size data collected from 1986 to 1992, when 21% of 2,500 samples fell between 600 and 800 microns, according to statistics analyzed by KSU animal science student Allen Baldridge. Samples were taken from feed samples and sent to the university for testing.

Table 1. Screen Sizes Used in On-Farm Hammer Mills and Resulting Micron Sizes
⅛ in. 5/32 in. 3/16 in. ¼ in. 5/16 in. ⅜ in.
Number of Samples 13 6 10 31 8 5
Low 647 685 689 677 812 1,233
Average 746 775 824 1,028 1,045 1,387
High 927 825 985 1,323 1,138 1,620

KSU swine nutritionist Mike Tokach points out that the recent data may be deceiving, as the majority of the samples come from feed mills and production companies that routinely monitor particle size.

Similar research was conducted by an Ohio State University (OSU) Swine Team. They analyzed ground corn samples from more than 60 pork producers and feed mills from 28 Ohio counties. The participating farms and mills feed about 580,000 hogs/year.

The team found that the average micron size of feed ground in a hammer mill was 916.5 microns. Roller mills averaged 720 microns.

The location of feed manufacture was also significant. On-farm processing yielded an average of 881.4 microns. Elevator-processed feed averaged 755.4 microns.

On-farm hammer mills produced a wide range of particle sizes. Study leaders Dale Ricker and Steve Moeller point out that while the average micron size was 746 with a ⅛-in. screen, there is a steady increase in particle size every time the screen size is increased. They point out that producers should use a 3/16-in. screen or smaller to get a hammer mill to grind corn to 700-800 microns. (See Table 1.)

The team also found a significant difference in average particle size of feed from on-farm or elevator-operated hammer mills. On-farm grinding averaged 1,029 microns and the elevator mills averaged 730 microns.

Economic Impact

The economic impact of particle size can be significant. For every 100 microns higher than the recommended range of 600 to 800 microns, the cost for feed efficiency is $0.50/finished hog. Therefore, if particle size is lowered from 1,000 to 700 microns, the savings is $1.50/hog marketed.

The OSU team estimates the economic impact to the producers participating in their study, who had average particle size greater than 800, at about $198,000 in lost efficiency.

“Keep in mind that feed prices are relatively low and that higher feed prices would have a much greater economic impact on producers,” Ricker says.

Particle-Size Testing

Particle size analysis can be performed by KSU at $10/one-half pound sample.

“The economic payback is great for a small economic investment,” Tokach says. “The number of samples needed for analysis depends on the amount of feed produced, however, we believe each mill should be tested at least monthly.”

For information on particle size testing at the KSU lab, call (785) 532-1277.

Ohio producers can get free micron evaluations by mailing or delivering samples to: Dale Ricker, OSU Swine Extension Associate, 219 S. Oak St., Box 189, Ottawa, OH 45875. For information, call Ricker at (419) 523-6294.