In most areas of the country, corn silage makes up a large percentage of a dairy cow’s diet. Producing high-quality corn silage is a process that involves several important steps. It starts with planting the right varieties that combine yield potential with ideal traits related to nutrient concentrations and digestibility. Next, the corn has to be harvested and stored properly to achieve a thorough fermentation. Finally, corn silage needs to be fed out appropriately to maintain nutritive value and hygiene from the bunker to the feedbunk.
Following these steps should result in a quality product. But is that finished product right for the rumen? Will it provide rumen microbes with the important components needed to help them do their job? Will it contain pathogens and toxins that could be detrimental to rumen function? If a silage isn’t right for the rumen, it’s not right for the cow, and health and productivity could suffer.
Here are a few tips to make sure the silage you are producing supports good rumen function.
Focus on fiber digestibility
Any forage that enters the rumen has to achieve a balance between being long enough to be “physically effective” (stimulate rumination) and being digestible enough for it to be thoroughly and efficiently broken down into components usable for rumen microbes and the cow.
With corn silage, there are hybrid types and harvest management considerations that can improve fiber digestibility, but they often come with a yield trade-off. You can plant highly digestible hybrids, adjust planting densities, harvest at an earlier maturity or increase cutting height to leave more stalk in the field. These practices may result in a corn silage that is more digestible, but yields per acre will likely suffer. If you have sufficient forage inventories, it might be worthwhile to look into a few of these strategies to create a high-powered corn silage for specific groups of cows.
Another factor influencing fiber digestibility is the “length of cut” which influences corn silage particle size. Silage cut too short will speed through the rumen without giving the rumen microbes the chance to thoroughly break down the fiber. Longer particles will take too long to break down and could limit intake. Cows will tell you when you have it right with consistent rumination activity, good manure consistency and sufficient milkfat production.
The ideal length of cut for corn silage would be 3/8-inch to 5/8-inch for unprocessed corn and 3/8-inch to 3/4-inch for processed corn. A shorter chop length for unprocessed corn may help break kernels and make more starch available in the rumen.
Watch starch availability
In addition to the fiber fraction of the corn plant, we can’t forget about the kernel fraction where starch is located. Digestible starch is an essential source of fermentable carbohydrates that drive propionate production in the rumen and feed the ruminal microbes that provide metabolizable protein (MP) to the cow.
The challenge is breaking into the corn kernel to get at the starch. Harvest timing is critical to capture the kernel at the right stage of maturity before the kernel gets too hard to break open. Harvesting corn at 33% to 36% dry matter (DM) is ideal to optimize both fermentation and ruminal starch availability. When corn silage is harvested at more than 40% DM, fermentation can be limited, and kernels get too hard to process thoroughly.
Judging when corn is at the right moisture level for harvest is critical to optimizing starch digestibility and has changed over the years as hybrids have evolved. An old rule of thumb was to break an ear of corn and look for the location of the milkline on the kernel. While that is still an indicator of when corn may be ready for harvest, the ability of stalk and kernel fractions to dry down at different rates has made it harder to hit the ideal harvest moisture using kernel milkline alone as an estimate of whole-plant moisture. Too much time can pass between the moment you recognize the plant is ready for chopping, and when you or your custom chopper can get into the field for harvest.
A better indicator is to chop a few plants, from different locations in the field, and to do a whole-plant moisture test. This is much more accurate and will give you a better idea of when corn is ready for harvest. It is recommended that you start testing whole-plant moistures three to four weeks before your anticipated harvest date.
Kernel processing is another important tool to improve starch availability. Closely monitoring extent of kernel processing throughout harvest is critical so you can catch any issues before that silage hits the bunker.
The amount of time your silage sits in storage is important, not only for achieving a thorough fermentation but is essential for improving starch availability as well. Also, kernel processing and length of storage interact to influence starch digestibility. A University of Florida study found that whole kernels in corn silage did not experience the same kind of starch digestibility improvement with storage that broken kernels did. So not only is it important to break kernels to increase surface area for better starch digestion in the rumen, but that starch will also get more digestible the longer the corn silage is stored. In the end, processing kernels and leaving silage in storage for as long as possible will help optimize starch digestibility once it gets to the rumen.
Prepare the rumen for change
Cows crave consistency, and silage changes can be disruptive. Unfortunately, change is inevitable as you move from last year’s silage to this year’s crop, so preparing the rumen for these changes is important.
Including refined functional carbohydrates (RFCs) in the diet can help provide the necessary stability. RFCs can help maintain rumen function and gut health while bolstering immune function which, together, can help the cow stay healthy and capable of fighting off challenges that may impact its health. Potential challenges could include mycotoxins from molds developed either in the field or in storage, pathogens like salmonella or pathogenic E. coli that may be present in the feed, and other disease challenges. Because forage changes may impart some level of stress on the cow, making the animal more susceptible to disease pressures, it’s important to include an RFC in the ration to help bolster a cow’s defenses and its overall resilience to pressures.
Corn silage is a tremendous source of digestible nutrients when grown, harvested and stored properly. Focusing on fiber and starch digestibility, and making sure the rumen is ready for any changes that may occur, will help you get the most of your corn silage crop.
