The following answer was provided by Pat Hoffman, University of Wisconsin extension dairy specialist.
Q: Does high-moisture corn chemistry change over time?
A: The short answer is “yes,” but this is an area that’s not well understood and research is beginning to explore the answers.
The dynamics are more important to know since the use of high-moisture corn on commercial dairy farms has grown significantly. For example, approximately 65 percent of Wisconsin dairy farmers now use high-moisture corn in rations.
Despite widespread use, it is an enigmatic feed because high-moisture corn per se is not a homogeneous feed. A specific high-moisture corn fed to a lactating dairy cow can be a highly variable feedstuff. That’s because corns of varying endosperm type can be ensiled between 20 percent and 40 percent moisture, with or without inoculants, at ambient temperatures of 10 degrees F to 70 degrees F, ensiled whole or ground, treated with or without organic acids, contain cob or husk, be fermented one to 365 days or more, stored in bags, bunkers and oxygen-limiting silos and still be classified as high-moisture corn.
Variance associated with high-moisture corn production practices have been hypothesized or shown to create variation in fermentation characteristics, chemical composition, starch digestibility and milk yield in lactating dairy cows.
Differences in ruminal, post-ruminal or total tract starch digestibilities between various grain sources and high-moisture corn can be generally categorized, but it has been challenging to link animal responses to high-moisture corn chemistry.
Recent research at the University of Wisconsin has focused on how high-moisture corn chemistry changes during fermentation and provides inferences as to why high-moisture corn starch digestibility in ruminants is altered compared to other grain sources such as dry corn.
One study monitored the fate of the starch protein matrix in high-moisture corn across a 240-day storage period. A second study evaluated the digestibility of high-moisture corn that was fermented and stored across a 240-day period using an in vitro gas production system.
The researchers found:
- The starch protein matrix in high-moisture corn is significantly altered by the fermentation process, especially the zein proteins which cross-link starch granules together.
- Fermentation-induced degradation of zein proteins in high-moisture corn appears to yield a general disassociation of starch granule clusters. This yields more individual starch granules and surface area for potential bacterial attack.
- Inferences from this investigation also suggested that the proteins in the starch protein matrix were more likely altered by bacterial proteolysis and may not have been simply solubilized by fermentation acids.
- Fermentation and storage time chronically increases the dry matter digestion potential of high-moisture corn.
- The degradation of the starch protein matrix in high-moisture corn seems to be chronic and slow.
- Traditional feed chemistry nutrients in high moisture corn (ADF, NDF, crude protein and starch) are static across the storage period and do not appear well-suited for determining biochemical factors that influence starch digestibility of high-moisture corn in ruminants.
- High-moisture corn is not a static feedstuff with a fixed of book value nutrient composition. Nutrient availabilities in it chronically change and these changes are likely dependent on physical processing, the strength of the starch protein matrix at ensiling, fermentation conditions at ensiling (dry matter and temperature) and the length of the storage period. Fermentation did not result in a simple convergence of high-moisture corn physio-chemistries for corns of different origins (hybrid, maturity, etc.)