On-farm sieving tests on dry and high-moisture corn provide dairy producers and nutritionists with helpful feed management suggestions for dairy rations. Particle-size assessments, like a grain sieve, provide information on the availability of starch for digestion by rumen microbial populations and intestinal enzymes. Knowing the “relative corn index” (RCI) score of corn can allow you to capture the greatest possible profit and optimize rumen health.
Knowing when it’s time to test
Use of grain sieves usually begins with observations of corn grain particles showing up in manure. During recent years of high corn grain prices, many dairy producers developed an acute concern for the cost of lost corn particles.
Testing manure samples for starch analysis is another way to determine the degree of grain losses, and research in this area indicates fecal starch over 5 percent is excessively high.
Particle-size assessments provide information on the availability of starch for digestion by rumen microbial populations and intestinal enzymes. A laboratory starch digestion report may indicate high starch digestibility.
Because the sample is ground for uniformity, it may indicate high starch digestibility that may not actually be present because cattle consume corn particle sizes that range from whole kernels down to powdered corn. If rumen microbes or intestinal enzymes can’t access the starch contained within corn particles, it will not be digestible.
Kansas State research determined that an on-farm four-sieve test method provides a simple, economical and quick determination of how well corn will be used by cattle. Dr. Mike Hutjens from the University of Illinois determined that on-farm grain particle-size assessments for dairy are best collected by using a series of four sieves and a collection pan.
The recommended sieve mesh sizes are #4 (4.75 mm), #8 (2.40 mm), #16 (1.01 mm) and #30 (0.54 mm). The test equipment can be purchased from several suppliers. The four-sieve field-test method was validated by making sampling comparisons against the 14-sieve system used by commercial feed testing laboratories.
Whole and coarse cracked corn will be primarily retained on the #4 screen and typical of what one might call “pheasant feed.” Cracked corn with a gravel appearance in manure will be retained on the #8 screen. A dairy grind-type corn is similar to a flour sifter and will be retained on the #16 screen.
A particle size typically found in swine feed will be retained on the #30 screen. Highly pulverized corn looking like powder will end up in the collection pan. Dr. Hutjens indicates that corn pulverized to this degree will digest similarly to that of 2 to 4 percent sugar-inclusion levels in the ration.
A basic rule of thumb is: Dry corn tends to have more than 50 percent of the particles retained on the #30 screen and that wet high-moisture corn (more than 30 percent moisture) tends to have over 50 percent of the particles retained on the #4 screen.
Dr. Hutjens collaborated with a Midwestern feed company to develop the “relative corn index” (RCI), which can be used to assess the utility of grain sieve distributions based on type of corn and other forage components.
Table 1 shows how to determine RCI, where the percent corn retained on each screen and pan is multiplied by the respective screen factor. The sum of the four-sieve and one-pan determination equals the RCI score.
What producers learn
Typically, corn with an RCI score less than 200 is more indicative of high-moisture corn and suitable when feeding rations with:
- High-moisture corn wetter than 30 percent moisture
- Corn silage greater than 30 percent starch
- High-starch rations (greater than 28 percent)
- Finely chopped forages
Typically, corn with an RCI score greater than 300 is indicative of dry corn and more suitable when feeding:
- Dry corn
- Corn silage lower than 30 percent in starch
- Modest-starch rations (less than 28 percent)
- Legume-based forages
- TMR with adequate particle sizing
Practical tips for testing success
Directions for conducting grain particle-sizing tests are as follows:
- Collect a grain sample that is representative, not biased with excessive fine or coarse particles. Sample size should be approximately 8 ounces or what amounts to two handfuls of grain.
- Place sample onto the stacked #4, #8, #16 and #30 screens along with the pan.
- Place lid on top of #4 screen.
- Shake horizontally and vertically until all grain on the #4 screen has been exposed to the openings.
- Remove #4 screen and weigh corn retained on screen. Record for calculations.
- Repeat steps 4 through 6 for the remaining stacked #8, #16 and #30 screens.
- Record weight of grain in the pan.
- After screen and pan weights have been determined, add them together and calculate percentages retained on each screen and pan.
- Compare findings to relative index score (RIS).
On-farm particle-sizing tests require a user to shake and inspect each screen in working through all the sieve sizes. Avoid overfilling the screen with grain (if the corn appears to be finely processed, then one handful is used initially).
Pay attention to the #30 screen, which can become plugged and filled with fine corn, preventing final separation. Use a smaller sample size to help mitigate the plugging problem.
More quantifiable sieving information can be gathered by submitting samples to commercial feed-testing laboratories that use the official American Society of Agricultural Engineers grain standards 14-sieve measurements for calculating the mean particle size (MPS) in microns and standard deviation (SD) of the sample.
MPS recommendations are 1,500 microns for high-moisture corn compared to 800 microns for dry corn. The SD should be less than 2.5, which is an indicator of how much of the corn is finely ground on one side of the average MPS compared to coarsely ground on the other side of the average MPS. The lower the SD, the more consistent is the grind size of the corn. PD
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Bill Seglar
- Senior Nutritionist
- DuPont Pioneer
- Email Bill Seglar
