By Bill Mahanna and Ev Thomas
Sometimes it takes a while for scientific understanding to catch up with what dairy producers and nutritionists intuitively know from observing cows and looking at manure. For many years, it has been a standard recommendation among nutritionists to wait until after Christmas to feed new-crop corn silage and high-moisture corn. Researchers have finally discovered a rational explanation for this decades-old recommendation.
Starch is the Culprit
It starts with the physiology of the corn kernel and changing rates of starch digestion (often referred to as the mathematical term, Kd). This is why feeding new-crop legume or grass silage soon after harvest is not a concern. The digestion issue revolves around starch rather than fiber, and legume/grass crops are essentially devoid of starch.
The November 2010 Feeding column “Why not all corn feeds the same” on page 765 detailed the anatomy of corn kernel’s endosperm which consists of starch granules encased in zein proteins. Concentrations of these proteins go up with kernel maturation and peak at the time of black-layer formation (about 35 percent kernel moisture). Mother Nature is concerned about the next generation and created these storage proteins with the ability to repel water in order to prevent premature starch hydration that could interfere with germination.
Given that Mother Nature never intended corn to be eaten by a dairy cow, these proteins present a nutritional challenge by interfering with starch digestion. However, over time in fermented storage, silage microbial activity and the chemical action of fermentation acids gradually solubilize the proteins freeing up starch granules for more rapid digestion by rumen microbes. This is why corn in silage or high-moisture grain has higher energy and is more ruminally available than the same hybrid fed as unfermented, dry corn grain.
As the corn kernels in corn silage or high-moisture corn (over 25 percent moisture) begin the fermentation process, they undergo the most rapid changes during the first two to three months in storage. It has now been proven in animal trials in both the U.S. and Europe that the rate of starch digestibility (Kd) is also changing rapidly over this period, providing the scientific basis for our long-held recommendations on waiting to feed new-crop silages.
Perhaps we need to talk more with our beef colleagues. Dairy nutritionists have now learned that for decades, feedlot nutritionists have relied on soluble crude protein (or nitrogen) content of high-moisture corn as a proxy for rate of starch digestion in feedlot cattle. This makes sense because as the zein proteins are gradually solubilized in fermented storage, the level of soluble protein should go up, as well. High-moisture corn with a protein solubility below 40 percent is generally from lowermoisture corn (with less extensive fermentation) exhibiting lower ruminal starch digestibility more similar to that of dry rolled corn. Feeding high-moisture corn with an N-solubility that exceeds 60 percent often results in more acidosis and incidents of steers going off-feed.
Continues to Drift
There is an abundance of corn silage fermentation research showing rapid changes in silages in the first two to three months of the ensiling process. This research lends credence to feeding recommendations of waiting until after Christmas. What was not understood until recently was what happens in longer-stored silages and grains. Timecourse studies with lab-scale research silos indicate that corn silage starch digestibility plateaus after about five to six months in storage. This finding is further supported by monitoring average protein solubility in corn silage samples submitted to commercial laboratories, assuming that protein solubility is highly related to starch digestibility.
High-moisture corn is a bit different. Both animal trials and protein solubility analysis show that high-moisture corn appears to continually drift upwards in starch digestibility out to about 12 months. The difference between corn silage and high-moisture corn is likely due to kernel maturity at time of harvest and the more extensive fermentation (pH) experienced by silage kernels.
Research studies have now validated what your nutritionist has been saying for years. If feed inventories allow, it is best to wait 2 to 3 months after harvest to begin feeding new crop corn silage and high-moisture corn. By doing this, you will avoid the rapid changes that make feed consistency an impossibility. Having enough silage on hand to allow for longer waiting periods to feed new-crop is an economic decision based on the inventory carrying cost of that feed. However, it appears that most of the rapid changes will have abated within the first two to three months.
Account for Improvements
It is important that nutritionists continue to account for the upward drift in ruminal starch digestibility (about 2 percent units per month) that occurs, especially in highmoisture corn, following the early dynamic period. Failure to account for starch Kd changes may explain some of the “spring acidosis” and milk fat depression seen on dairies feeding high levels of corn silage in conjunction with high rumen fermentable high-moisture or steamflaked corn.
This article was originally published in January 2011 Hoard’s Dairyman issue, and is reproduced with their permission.