Kansas State University (KSU) researchers devise three-screen method to add accuracy to feedgrains.

KSU graduate student Crystal Groesbeck, who oversees the school's particle size analysis program, and Cassie Benz, an undergraduate research assistant, conduct hundreds of grain particle size analyses for pork producers across the United States each year.

Those producers, their veterinarians and nutritionists are all well aware that reducing particle size increases the relative surface area of the feed material, thus allowing for greater interaction with digestive enzymes.

The improved digestibility results in improved average daily gain and feed efficiency. Better digestibility translates into fewer nutrients in swine waste — a plus for the environment.

“We encourage producers to target 700 microns particle size with an acceptable range of 650 to 750 microns,” says Groesbeck. Research shows that for every 100 microns over 700, producers lose 50 cents/pig due to reduced feed conversion.

Fact Sheet Describes New Test

The one-screen method currently available for determining particle size does not provide as accurate results as the standard procedure used in commercial labs.

“The standard equipment for testing particle size is relatively expensive to purchase and maintain, and the total analysis can be rather time-consuming,” says Benz.

The one-screen method generally results in underestimating actual particle size, and may give producers a false sense of security regarding particle size, while the three-screen method is more accurate, Groesbeck explains.

KSU researchers evaluated and demonstrated better accuracy with a three-screen particle size testing system. The work led to development of a producer fact sheet, which tells how to purchase and operate the equipment. A spreadsheet is used to analyze the results and create a chart of grain particle size over time.

“By charting your results, you can see when grinding equipment needs maintenance,” explains Benz.

The fact sheet, found at www.asi.k-state.edu (click on “swine,” then “extension”), includes the four main steps to achieve proper testing of particle size. The steps are described in the accompanying sidebar on page 23.

Defining the Elements

Two key elements of the three-screen procedure include the use of balls and carnucles to help shake the feed material down through the sieves, say KSU researchers.

Balls are marble-sized rubber balls that roll and bounce up and down during the shaking process. Carnucles are a miniaturized version of a scrub brush. These travel back and forth over the screen and also help material fall through.

“A lot of people don't necessarily know about balls and carnucles in particle size analysis and they are really important,” stresses Groesbeck. “We see about a 100-micron difference when we run a sample with them vs. without them.”

She says a second important consideration is ensuring that the screens are cleaned after each use and thoroughly washed in soapy water after taking about 50 samples.

“The small screens get clogged up with particles over time, and clog even faster if we do samples of complete feed with added fat,” notes Groesbeck. “That's why we ask producers to send in samples of ground grain rather than complete diets.”

If particle size test results on the histogram depicting the percentage of particles on each screen don't extend across all screen images, that's an indication the screen may need to be cleaned.

Testing Frequency

Stationary mills and feedmills should check ground grain samples weekly and submit samples for a particle size analysis once a month to a commercial lab with a full, 10- to 13-screen tester, the researchers suggest.

Producers with portable grinding feed equipment may test grains every other week and send in a sample every other month.

A number of commercial labs and feed companies routinely test feed for particle size.

KSU also analyzes samples at a cost of $10/sample. Send a small zip-lock bag of ground grain (1 lb. maximum) to KSU Swine Lab, Room 206 Weber Hall, Department of Animal Science, Kansas State University, Manhattan, KS 66505, with “Attention: Particle Size.” Include your e-mail address for faster response.

For more information, go to the KSU Extension Web site or contact Crystal Groesbeck by phone (785) 532-1277 or e-mail cgroesbe@oznet.ksu.edu.

Four Steps to Achieving Proper Particle Size

Kansas State University (KSU) graduate student Crystal Groesbeck and undergraduate research assistant Cassie Benz developed the following procedure:

  1. Set up sieves by placing one ball and one carnucle in sieve #30, one ball and two carnucles in sieve #50, and no balls or carnucles in sieve #12 or the pan.

    Weigh the empty sieves with balls and carnucles, and record the empty weights of each. Stack the sieves on top of the pan in increasing numerical order so #12 is on top and #50 is on top of the pan (Figure 1).

  2. Weigh 50 grams (1.75 oz.) of an accurate representation of the sample to be tested and pour it into the top sieve (#12). Securely place the cover on the sieve stack and shake vigorously from side to side by hand for 90 seconds (Figure 2).

  3. Weigh the sieves with balls, carnucles, and sample collected on each sieve, and record the gross weight (Figure 3).

    Then enter the initial weights of sieves into the Microsoft Excel worksheet (also available at www.asi.k-state.edu). This will automatically compute the net sample acquired by each sieve and calculate the particle size of the sample.

    It will also plot this particle size on the monitoring graph to easily track variations in particle size.

  4. Thoroughly clean the sieves before running another sample. The best method of cleaning sieves is with a sieve brush and compressed air to blow particles through sieve openings.