Bank on corn silage in your rations

By Dr. Darin Bremmer
Looking back a number of years, it was rare to feed a milk cow diet with more than 50 percent of the forage dry matter (DM) coming from corn silage.  Today, it’s common to feed diets with at least 80 percent of the forage DM coming from this crop.

That pushes us to ask:  Can a majority – or even all – of the forage DM come from corn silage?

Advantages of corn silage
Several factors have led to feeding higher corn silage diets.

First, it is easier to put up one consistent crop of corn silage than it is to put up three to five consistent crops of haylage.  Each crop of haylage has its own unique characteristics that must be considered when developing the diet.  In contrast, once a high corn silage diet is dialed in, it generally requires very few changes throughout the year.

We also want to get the most value from every acre.  This is especially important as herds expand and the land base doesn’t grow proportionately.  Corn silage is the highest yielding forage; we typically achieve at least 8 tons DM per acre.  We struggle to reach yields of 5 tons DM with alfalfa.

Carryover is important
If feeding fresh corn silage in a high corn silage diet, it’s common to see milk production drop an average of 6 pounds from October through December.  That’s due to low starch digestibility.

Starch digestibility improves with time in storage.  Bacteria need time to break down the prolamin protein linkages that encapsulate the starch.  This process takes about three to four months in storage before the digestibility begins to improve.  For that reason, a realistic goal is to have enough carryover to be fed through January or February.

Carryover not always an option
Although a carryover period of three to four months is ideal, it’s not always an option.  Expansion or weather challenges can deplete your carryover.  A few alternatives can help you address this challenge by maximizing starch digestibility earlier.

• Excellent kernel processing:  Pulverizing the kernel exposes a greater kernel surface area and improves starch digestibility.
• Short-day varieties:  Short-day corn is typically chopped slightly immature, so the plant has less time to form prolamin linkages.
• Varieties with higher starch digestibility:  Corn varieties can be selected for higher starch digestibility.  This starch is flourier and contains fewer prolamin linkages.

Other nutritional considerations
Corn silage passes through the rumen more quickly than alfalfa or grass silage.  When feeding a high corn silage diet, you need enough physically effective fiber to maintain a good rumen mat.  This slows the rate of passage, stimulates cud chewing, and improves rumen fermentation and digestion.

Although poor starch digestibility is an issue with new corn silage, we can also have issues with very fast starch digestibility if the crop has been in storage for at least six months.  Highly digestible starch can cause a rapid drop in rumen pH, potentially leading to depressed milkfat synthesis.  In this case, your nutritionist may adjust the amount of starch, starch sources and other ingredients.

Another issue is low potassium with little or no haylage in the diet.  For close-up cows, we want to feed low potassium diets to prevent milk fever.  However, we want higher levels of potassium in milk cow diets as research shows this may improve milk production and milkfat synthesis.  Delactose permeate, whey permeate, molasses, potassium chloride or potassium carbonate may be added to boost dietary potassium.

Economic trade-offs
Some argue high corn silage diets aren’t worth it because you must feed more protein if you take out alfalfa.  While that’s true, a lot more goes into balancing these diets than simply adding protein.

For example, corn silage contains up to 40 percent starch on a DM basis.  That means you can feed less corn grain, freeing space in the diet.

In addition, you can add the less expensive rumen-degradable proteins sources (corn gluten, canola meal or soybean meal) instead of the more expensive rumen undegradable protein sources (blood meal, heat-treated soy products, etc.).

Many factors must be considered when moving to higher corn silage diets.  However, doing so can have significant economic benefits for your farm.  Work with your consultant to develop a strategy that best fits your farm’s goals.

This article was originally written for the October 25, 2014 issue of Hoard’s Dairyman.

About the author:  Dr. Darin Bremmer grew up on a farm in Shannon, Illinois. Af­ter high school, he attended the University of Wisconsin-Platteville and received a bachelor’s degree in animal science in 1993. From 1993 to 1995, he attended the University of Illinois and received a master’s in animal science with an em­phasis in ruminant nutrition. Bremmer then completed a Ph.D. in nutritional sciences with an emphasis in animal nutrition and a minor in dairy science from UW-Madison in De­cember 1999. In Dr. Grummer’s labora­tory at UW-Madison, Bremmer’s research focused on transition cows, studying ketosis and fatty liver. After completing his Ph.D., Bremmer worked for a major feed company as a dairy nutritionist and technical services manager in Wisconsin. In March 2003, he joined Vita Plus as part of the dairy nutrition and technical services team based in central Wisconsin.