High-moisture corn (HMC) changes during the ensiling process; it appears that the proteins in the starch-protein matrix are altered by bacterial proteolysis during an extended ensiling time.

This has important implications for feeding, because degradation of the proteins allows the rumen bacteria in cows to have greater access to the starch granules that are embedded in the starch-matrix complex — at least that's the hypothesis of researchers at the University of Wisconsin who published their research in this month's edition of the Journal of Dairy Science.

While substantiating that protein degradation does take place during ensiling and fermentation, the study discounts the role that commercial inoculants may play in the degradation process.

"Degradation of hydrophoboic zein proteins in the ensiling process appears to be best explained by chronic proteolytic activity because inoculation, which yielded greater lactate and acetate concentrations in HMC, had no effect on the degradation of hydrophobic zein proteins in HMC," the researchers said.

So, the role of inoculants is to improve the fermentation profile of the high-moisture corn, not alter the starch-protein complex. And, it is important to consider the dynamics at play.

High-moisture corn is not a static feedstuff with a fixed book value of nutrient composition, points out Pat Hoffman, dairy scientist at the University of Wisconsin research facility in Marshfield, Wis. Its nutrient content changes during storage, and these changes are likely dependent on physical processing, the strength of the starch-protein matrix at ensiling, and the length of the storage period. Different hybrids with different harvest maturities can come out of the silo with different feeding values.

The fermentation process does not necessarily homogenize them and may, in fact, cause greater differences, depending on storage conditions. Since high-moisture corn is dynamic, it is important to monitor starch digestibility and availability during feedout to avoid negative effects like SARA.