Grain and kernel particle size: The math – Pat Hoffman, Vita Plus

Click here for Hoffman’s PowerPoint presentation.

Progressive forage harvesters spend a lot of time looking at and adjusting for the kernel processing score (KPS) of corn silage.  But, according to Pat Hoffman, Vita Plus dairy technical specialist, “all the cow sees is surface area.”

During his presentation at the Vita Plus Custom Harvester Meeting, Hoffman described what it takes for a cow to use the starch in corn silage and, ultimately, make milk with it.  He said dairy producers are very focused on KPS because it’s easy to see corn – and how much it’s broken up – in the silage.  And, if calories from starch are reduced in the ration, a decrease in milk production can follow within 12 hours.  In contrast, Hoffman said responses to a mineral or protein change will likely be much slower and harder to pinpoint.

Hoffman described KPS as “not very absolute and not very perfect,” noting that, while it is important, a lot more is going on than just the processing score.  For example, he said the ideal KPS for corn silage is moisture-dependent.  A good rule of thumb is to double the dry matter (DM) content and subtract 5 to get the target KPS for that specific silage.

Kernel processing “gives a little jump in what starch is digested in the rumen,” Hoffman said, but fermentation has a much greater impact.  Hoffman likened processing to a maul and fermentation to a jackhammer.  Bacteria cannot colonize on the pericarp tissue (seed coat), but they can colonize inside of it when a kernel is broken open.  Once the silage bacteria can get into the kernel, they go to work on the prolamin protein matrix, which encapsulates the kernel’s starch.  During fermentation, silage bacteria are responsible for the “particle decay” or breaking down this matrix to make the starch available.

“The prolamin matrix is like the wrapper on a candy bar,” Hoffman said.  “You can’t digest the candy bar easily if it still has the wrapper on it.”

After adequate fermentation time, a corn kernel will smear between your fingers because the protein structure has broken down.  This is why nutritionists often back corn out of the diets in January or February; the corn silage has had time to ferment and the starch is now readily available to the animal.

Hoffman concluded his presentation by offering particle size guidelines for various corn feedstuffs:

• Corn silage:  1,800 to 4,000 microns (the drier the corn silage, the finer the corn should be)
• High moisture corn (HMC):  600 to 2,800 microns (similarly, the drier the corn, the finer the HMC should be ground)
• Snaplage:  1,400 to 2,200 microns (due to husk and cob inclusion, finer processing is required to aid in packing the silo)
• Dry corn:  Grind very fine