Research shows a faster shaking frequency is better than a slower one when using the recently modified Penn State Particle Separator.

How fast should you shake the new three-screen Penn State Particle Separator? About 1.1 Hertz, or 66 forward and backward movements per minute, according to research reported in the May Journal of Dairy Science.

Researchers at Penn State University examined the effect of three shaking frequencies — 0.9, 1.1 and 1.6 Hertz (slow, medium and fast) — on the particle size of alfalfa haylage, corn silage and TMR samples. One Hertz is equal to the number of full forward and backward movements within one second, says Paul Kononoff, a dairy nutritionist with Renaissance Nutrition in Roaring Spring, Pa., and former Penn State graduate student at the time of the study.

The results show that reducing the shaking frequency from 1.1 to 0.9 Hertz caused a greater percentage of particles to stay on the top screen compared to the two screens below it. (The top screen measures 19 millimeters, the middle screen measures 8 millimeters and the new bottom screen measures 1.18 millimeters.) Consequently, the mean particle length (MPL) of samples shaken at a rate of 0.9 Hertz also was greater than that of samples shaken at a frequency of 1.1 Hertz, Kononoff says. In contrast, increasing the shaking frequency from 1.1 to 1.6 Hertz did not significantly alter particle size. Results for the TMR samples used in the experiment are shown in the table below.

As a result of these findings, the researchers recommend shaking the particle separator at a rate of 1.1 Hertz or greater with a stroke length, or distance, of 17 centimeters when analyzing forage particles.

You can compare your shaking frequency to this recommendation by dividing the number of full forward and backward strokes by the time that it takes in seconds to perform them. For example, if you achieve 66 full forward and backward movements within 60 seconds, your shaking frequency equals the recommended 1.1 Hertz (66 strokes divided by 60 seconds = 1.1 Hertz).

Shaking frequency





Percent of TMR particles1

Greater than 19 mm




19.0 - 8.0 mm




8.0 - 1.18 mm




Less than 1.18 mm









1TMR contained 50:50 forage-to-concentrate ratio and 9.5 percent grass hay, 25.3 percent corn silage and 14.6 percent alfalfa haylage as a percent of dry matter.


2MPL = geometric mean particle length as calculated by the American Society of Agricultural Engineers (2001).