Crop processors on forage harvesters don't always do the job right. That's according to a new test that determines how much of the starch in corn silage has been processed for adequate digestion.

The test was introduced late last fall by Dairyland Labs, Arcadia, WI. By mid-August, 33% of the hundreds of samples sent to the lab were underprocessed, says Dave Taysom, Dairyland Labs director.

“I'm surprised the percentage was that high,” says Taysom. “The producers who sent those samples could benefit the most from evaluating their harvesting techniques.”

Submitted silage samples are dried to 7-8% moisture, then shaken in a pan with nine sieves, each with different-sized openings. The amount of particles collected on each sieve is measured. Particles greater than 4.75 mm (about ¼") are considered coarse, 1.18-4.75 mm particles are medium and all others are fine.

After a laboratory starch analysis, each sample receives a Corn Silage Processing Score (CSPS) — the percentage of starch that has been sufficiently processed. If more than 70% of the starch passes through the coarse screens, processing is optimal. If the silage scores 50-70%, it's considered average; a score of less than 50% is inadequate.

Last month, Tom and Doug Block sent the lab a sample that was in the underprocessed category. The brothers' nutritionist, Jim Barmore, suggested they use the test after they opened a new bunker at their 600-cow dairy near Pearl City, IL.

The men could see that the silage coming out of that bunker wasn't well-processed. Barmore thought the analysis would help in ration balancing, Doug Block says.

Block knows why that silage was inadequately processed. “As we got toward the end of harvesting, the weather was starting to change and we were pushing hard to get done. If we had to do it over again, we would have paid more attention.”

The Blocks blame themselves, not their long-time custom harvester. “We all work together as a team,” Block says.

Barmore, who owns Five-Star Dairy Consulting in Verona, WI, made adjustments to the ration to compensate for the underprocessed silage.

“I cut back on the corn silage, realizing it had a discounted energy value, and added corn gluten feed to try to bring a little more digestible fiber into the ration,” he says.

Water was added to increase the TMR moisture level and minimize sorting.

While those ration adjustments are important, Barmore encourages producers who test their corn silage to keep their eyes on the big picture.

“Don't get hung up on a specific number, rather look at the trends,” he says. “Use that information to discuss your goals for particle size, moisture and overall corn silage quality with your harvester and staff.”

To ensure proper processing, Barmore recommends the following:

  • Adjust the processor so it rolls or crushes over 95% of the kernels and breaks cobs into thumbnail-size pieces or smaller. There should not be any full cob disks.

  • Harvest at the proper moisture content. “Typically, 65-68% is ideal.”

  • Use a 3/4" length of chop for non-brown midrib hybrids.