Things to Keep in Mind Before and During Corn Silage Harvest

By Daniel Hudson, UVM Extension Agronomist

  • On warm, dry, breezy fall days, whole plant moisture can drop up to 2% per day.  If you have not done so already, check the maturity and moisture level of your corn. Aim to harvest within the 30-35% dry-matter window.
  • If you have a bumper crop, consider chopping higher for a higher energy corn silage product that can help you reduce your feed bill.
  • Depending on whether you have a kernel processor, keeping the theoretical length of cut between 3/8” (without processing) and 3/4” (with processing).
  • Keep in mind all the ways “shrink” happens on the farm and take steps to minimize losses.

    Picture from Iowa State University

  • When packing, don’t hurry, and make sure you have enough tractor weight to get the job done well: total tractor weight (for all continuously packing tractors) divided by 800 equals the number of wet tons you can pack per hour.
    • Oxygen exclusion will be maximized when: plastic is thicker; multiple layers are used; an oxygen barrier is included; and if the covering is adequately weighed down (tires should be touching).

Once the seeds are in the ground, your theoretical yield maximum is established.  Good decisions (weed control, N rates, etc.) will keep you nearer that theoretical level maximum.  The same can be said about corn silage quality: once the corn is at the proper moisture for harvest, the quality maximum is established and it only goes down from there.  Further, once it is in storage, there is a theoretical maximum quantity and quality that will actually enter the digestive tract of your animals, and many places for it to be lost. As with most things, it is the little things that add up to make a big difference: poor silage-making and silo management practices can cause losses of 40% between the field and the digestive tract of your cows.   Here are some things you can do to reduce losses on your farm:

Start on time: We often think of whole plant corn silage drying down at a rate of 1/2%? per day; on warm, dry, breezy fall (or late summer) days, whole plant moisture can actually decrease by 2% per day, and the optimal point to begin harvest can sneak up on us.  This is particularly likely after a hot summer.  Silage made from over-mature corn affects quality in several ways that combine in various ways to harm your bottom line: higher fiber, lower digestibility, more shrink (difficult to pack, more oxygen entrapment and spoilage).  For bunker silos, harvesting the corn when it is 30 – 35% dry matter will maximize the opportunity for attaining a packing density of 15 lb/ft3or more.

Cutting height: This obviously does not pertain to shrink, but needs to be mentioned (again).  Corn prices are at record high levels.  You could offset some of that cost by chopping your corn higher than usual.  That will obviously result in a lower total yield, but many farmers in some parts of the Northeast have the best corn crop that they have ever had.  The choice may be between chopping higher to improve quality and reducing your grain bill, or chopping low and having enough corn silage to sell.  Depending on where you are, selling corn silage may not be as easy as it is in some years.

Understand “shrink”: If a couple of cucumbers spoil in the refrigerator once in a while, nobody gets too upset.  If 40%+ of the food is lost or spoiled, the household managers tend to get excited.  Brian Holmes, a University of Wisconsin Extension agricultural engineer demonstrates that even under ‘good management’ 18% of the harvestable corn silage in your field never makes it into the digestive tract of an animal.  Under ‘not so good management’ almost 29% will never make it into an animal. Using a spreadsheet (see references below), Holmes neatly demonstrates that on an 85 cow dairy, the difference between 19 and 29% loss amounts to almost $17,000/year!  Sources of loss include harvest, filling, storage, storage feed-out, and feeding practices.

Chopping length and kernel processing:  Fermentation is an anaerobic process.  The more air space you have among particles in the silo, the more spoilage you can expect.  Crop processors allow kernel-cracking to take place without having a suboptimal theoretical length of cut (TLC).  Without a crop processor, a 3/8” TLC is necessary to adequately damage the kernel to optimize starch utilization in the system.  With crop processors, the TLC can be increased without affecting starch digestibility; while increased fiber length improves rumen health, having a TLC longer than 3/4” makes achieving an optimal packing density more difficult.  Kernel processing improves starch utilization and reduces cob fragment size to prevent sorting during feeding.  Limin Kung, Jr., a noted silage expert from University of Delaware, suggests that processing is adequate if 90-95% of kernels are cracked or crushed (70% less than 1/4 kernel size) and if the cobs are in at least 8 pieces.

Packing: Chopped corn often shows up at the bunker faster than we think.  Packing layers should be less than six inches thick to prevent excessive trapping of oxygen.  A University of Wisconsin formula suggests that the number of wet tons of silage a continuously packing tractor can adequately pack can be determined by dividing the weight of the packing tractor by 800.  If packing is your bottleneck, it is better to add weights to the tractor, add another tractor, or slow the chopper down rather than to inadequately pack the material going into the bunker silo.  Keep this in mind if you are using custom harvesters who may be able to harvest much faster than you can pack.

Covering to Exclude Oxygen:  Some farmers do not cover their bunker silos, others plant rye on top, thinking that will help somehow.  Inadequate oxygen exclusion from the top can lead to storage losses over 30%!  White plastic is better than black (lower temperature), thicker (8 mil) is better than thin plastic (4 mil), two layers are better than one, and oxygen-barrier plastic is ideal.  The covering will not function as intended unless it is weighted down adequately.  A well-weighted cover that includes an oxygen barrier may have as little as 1-2” of spoilage on the top compared with 12” in poorly covered or uncovered bunker silo.

For the most part, the biological shrink between the field and the digestive tract of the animal is due to microbial degradation of highly digestible nutrients.  The only way to compensate for low quality feed is to purchase grain.  Take an inventory of each step of your silage making practices and note opportunities for improvement.  This will be a giant step towards keeping your feed costs as low as possible.

Sources used to prepare this document include:
Donna Amaral-Phillips (University of Kentucky): Harvesting Methods for Corn Silage Affect Performance

Faith Cullens and Craig Thomas (MSU Extension): Managing Corn Silage Harvest and Bunk for Nutrient Retention:

Patrick C. Hoffman and David K. Combs, (University of Wisconsin): Managing Aerobic Stability in Silages and High Moisture Corn:

Dr. Brian Holmes (University of Wisconsin): Determining the Value of Improved Silage Management:$$%207-8-11.xls

Dr. Limin Kung, Jr. (University of Delaware) An Update on Silage Management (video)

Dr. Limin Kung, Jr. (University of Delaware): Practical Management Aspects of Corn Silage Production for Dairy Cattle:

Dr. Bill Mahanna (Iowa State, Pioneer Seed): Cost of Shrink Must be Communicated

Erin E. McDonell and Dr. Limin Kung. Jr., (University of Delaware): An Update on Covering Bunker Silos:

Dr. Bill Weiss (OSU Extension) Corn Silage Harvest


About Daniel Hudson

Daniel is an agronomist for University of Vermont Extension in the areas of agriculture and nutrient management.
This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s