Many producers have completed corn silage harvest and some may be near to or already harvesting high moisture shell corn. If you plan to incorporate HMSC into your feeding strategy, the following three factors can help you get the most from this high-value feed.

Processing, particle size
    Like corn grain, processing HMSC increases surface area so that microbial digestion can take place. The ideal particle size for HMSC is interdependent on moisture and storage time, which we’ll discuss next. A mean particle size of 1,200 to 1,500 microns is recommended for HMSC at 30% moisture. The drier the HMSC, the finer the grind needs to be.
    The two most common HMSC processing methods available are hammer mills and roller mills. In a hammer mill, particle size is determined mostly by screen hole size. The screen prevents the ground feed from leaving the grinding chamber until it reaches a given size. In a roller mill, feed passes between rolls, and is sheared and compressed to reduce the particle size.
    Both systems will do a great job of processing HMSC if they are set up properly and receive regular maintenance. Roller mills can handle high moisture levels a little better; a hammer mill is more effective at reducing particle size if moisture levels are lower than ideal. Our 2021 growing season has generated significant variation in kernel size and moisture in areas impacted by the drought. More frequent adjustments may be needed to achieve desired HMSC particle size.

Moisture
    The University of Wisconsin recommends targeting 28% to 32% moisture for HMSC. Storage structures may dictate your target value. For optimum starch digestibility, a little too wet is better than too dry. If you will start feeding HMSC immediately after harvest, you may want to consider segregating two- or three-months’ worth of HMSC with slightly higher moisture. This will provide a more immediate source of highly digestibly starch.
    Success at low moisture values is often dependent on the degree of processing and the integrity of the storage unit. In a perfectly maintained, oxygen-limiting unit with a bottom unloader, 20% to 25% moisture may be acceptable, but is still a little on the dry side.

Storage time
    Allowing adequate storage time for wet corn is the greatest supporter of starch availability. Prolamin-zein proteins encapsulate corn starch and act as a barrier to digestion. Over time, protease enzymes (produced by proteolytic bacteria) break down this protein matrix, making starch more available. The wetter the corn source, the quicker this process occurs and the sooner the feed will reach its full starch digestibility potential.
    For example, HMSC ensiled at 24% moisture will have less proteolytic lactic-acid bacteria (LAB). Thus, it will take longer for prolamin proteins to degrade and degradation will occur to a lesser extent. If it is also coarsely processed (greater than 2,000 microns), starch digestion will be very slow and the potential for excessive fecal starch will be high.  
    In contrast, HMSC ensiled at 35% moisture may ferment very rapidly with a robust growth of LAB and, if finely processed (less than 1,000 microns), may result in excessively fast ruminal starch digestion. This may lead to rumen acidosis or decreased milk component production.
    The most important thing to remember is there is no such thing as a universal HMSC. The digestion of HMSC is dynamic, dependent on processing, and especially dependent on the intensity of LAB growth and length of storage. HMSC may feed poorly in the fall, feed well in the spring and become excessively digestible in the rumen the following summer. Because the digestibility of HMSC is a moving target, having enough carryover in your inventory will help you reduce this variation. Harvesting at the desired moisture and reducing particle size will also help you maximize starch digestibility of your feeds.
    Barry Visser is a nutritionist for Vita Plus.