The ruminal availability of starch in corn silage varies according to the hybrid and increases with processing level, crop moisture level and ensiling time. Starch digestibility is positively correlated with milk yield,1 making it an important factor to consider when harvesting and storing corn silage.
Well-processed silage can make starch more easily digestible. Kernel processing scores help producers assess their processing level. It’s generally recommended scores should exceed 70 percent, which indicates that 70 percent of the kernel particles passed through a 4.75 mm sieve.
If there is an extended harvest period, bear in mind that keeping an eye on the processing efficiency is more important in higher dry matter (DM) silage crops and less so if DM is at or below the lower end of acceptable.
Fresh silage may have lower starch digestibility — especially when harvested above 35 percent DM.
In addition, high-moisture corn (HMC) comes from the field at harvest time with a high population of natural microorganisms including bacteria, yeasts and molds. HMC can easily become aerobically unstable during feedout due the growth of wild yeast populations when the storage structure is opened and exposed to oxygen. These organisms use up the most digestible nutrients first and so can cause reductions in the digestible starch levels.
One key step to prevent instability at feedout is to use a silage inoculant proven to help maintain stability. For instance, Lactobacillus buchneri 40788, applied at a minimum of 400,000 colony-forming units (CFU) per gram of silage or 600,000 CFU per gram of HMC, is the only inoculant bacteria strain reviewed by the FDA and allowed to claim improved aerobic stability.
With increasing storage time, the silage becomes more digestible. Long-term storage gives enzymes time to break down proteins (prolamines) to make starch more available for digestion.
If possible, keep forages ensiled for a minimum of four months to allow the natural ensiling process to improve starch digestibility.
1 Kung L and Hallock S. Unlocking the potential of starch in corn silage and high moisture corn. University of Delaware presentation. Accessed June 26, 2017.