Producing high-quality wet forage is both an art and a science, mixed with more than a pinch of luck. By understanding the science behind it, the art can be perfected and the need for luck minimized.

Corn and small grain silages, with their low protein levels and high levels of available sugars, are easier crops to ensile successfully than alfalfa and grass haylages. Ensiling a wet forage involves chopping it to a suitable length, at an acceptable moisture level for the method of ensiling, then packing it as densely as possible in order to exclude oxygen, and finally sealing it as quickly as possible to prevent oxygen and moisture entering back into it. This starts an anaerobic fermentation phase where sugars in the crop, in the absence of oxygen, are converted to lactic acid. The pH of the ensiled material then drops to a level that eventually inhibits all microbial activity and thus “pickles” and stabilizes the silage.

Variety choices
How you deal with different varieties at harvest will affect your bottom line. If you have chosen a combination of varieties, don’t mix them together. Store them separately so you can take advantage of their individual qualities.

Let’s say that you’ve planted some brown mid-rib – a very digestible, high milk-per-ton type of silage – plus some more conventional, high-yielding, high milk-per-acre but slightly less milk-per-ton variety. You need to feed the brown mid-rib product to your transition, fresh and high-group cows. These cows have limited dry matter intakes and these types of highly digestible forages enable you to maximize their forage intakes while maintaining a nutrient-dense ration. You’ll keep your cows healthy and lower your feed bill.

Moisture drives digestibility
Ultimately, though, the most important factor driving the digestibility of your corn silage is its moisture level at harvest. This is usually directly related to its maturity in terms of whole-plant neutral detergent fiber (NDF) or total fiber levels, lignin levels (which is basically wood) and cob/kernel hardness.

Traditionally, cutting time for corn silage has been determined by tracking the milk line movement in the kernel. But this doesn’t always reflect whole-plant moisture levels, and with new hybrids this measurement can be way off. Chop too wet and you could get poor fermentation and excess dry matter loss due to seepage and run-off. Chopping too dry leads to difficulty in packing the material and prolonged fermentation which, again, will be the cause of large dry matter losses.

For a more accurate assessment of maturity, you should chop a strip of the corn crop when the milk line has just appeared in the kernel. Run a moisture test on this material, then estimate the actual harvest date by assuming a 0.5 to 0.75 percent per day drydown rate, aiming for an optimal 35 percent dry matter for ensiled material.

Processing advantages
You should aim to process your corn silage if possible. This virtually eliminates both whole kernels passing through the cow undigested and discs of cob material left in the bunk as refused feed. Some trials have shown that processing increases milk yield by 2 pounds or more a day but, in other trials, the difference between processed and unprocessed silages have been inconclusive. However, processing ensures better utilization of your silage and undoubtedly gives you more milk per ton of this valuable crop.

If you process your corn silage, set the roller clearances between 1 and 2 millimeters on your harvester and your theoretical length of cut (TLC) at 3/4 inch. Monitor processing throughout harvest because, as the crop dries out, the rollers may need tightening to keep processing efficiency consistent. For silage that is not going to be processed, chop it at a shorter TLC around 3/8 inch to ensure adequate kernel damage to maximize starch utilization.

Fill bunkers as quickly as possible in a “progressive wedge” fashion, which minimizes the amount of ensiled crop exposed to the air. Build silage piles in layers no more than 6 inches deep and pack thoroughly. Always make sure you have enough packing vehicles on the pile or bunker. Good compaction is absolutely essential for profitable silage production. A Kansas State study showed that packing at 10 pounds per cubic foot of dry matter density can lose up to 20 percent of the dry matter you spent so much time and money to ensile. Conversely, they showed by packing to a 20 pound per cubic foot of dry matter density, the dry matter loss will halve to only 10 percent.

Preservation additives
The next decision is whether to use some kind of additive to speed up the preservation process of your silage. There are plenty to choose from:

• Organic acids that literally pickle the crop as it is chopped.
• Oxygen-scavenging chemicals that help accelerate the silage into its anaerobic phase of fermentation.
• Oxygen-scavenging and lactic acid-producing bacteria that use the sugar in the crop as a substrate to flood the crop with preserving lactic acid.
• Propionic acid-producing bacteria that help preserve silage shelf life after the bunker is opened up.
• Enzymes that help break down the starch and fiber in the crop to simple sugars. This gives bacteria (either added or naturally occurring) a much larger supply of substrate for producing lactic acid. Sugar sources like molasses have been used for the same reason.
• Anhydrous ammonia has been used on corn silage as a means of killing fermentative microbes. This effectively sterilizes the silage while at the same time adds nonprotein nitrogen (NPN) to what is normally a low-protein crop. This last process can be hazardous and it is certainly safer to add a little urea into the feed if the ration calls for some NPN.

Of all these additives, the bacterial inoculants are undoubtedly the most popular. Ask for the science behind any product offered to you. Most bacterial products should supply 100,000 colony forming units (CFUs) of lactic-acid-producing bacteria (LABs) per gram of ensiled material. Making an extra source of sugars available to the “bugs” can speed up the fermentation process, and enzyme addition is the easiest and cheapest way to achieve this.

Silage between the sheets
Your final decision is not whether to sheet down your silage crop, but whether to use an oxygen barrier, under sheet, as well as a regular 6-mil gauge, white plastic sheet. These extra sheets are very effective in eliminating waste at the top of the pile or bunker and are definitely worth considering.

There’s also an alternative to weighing down these sheets with tires. It’s a heavy plastic netting that applies even, downward pressure on the sheeting, allows water to run off, and offers protection against possible physical damage from animals, birds, machinery and hail. Whichever method you choose to weigh your cover sheet down, don’t cut corners.

At all of these stages, speed is of the essence. You have to minimize the crop’s exposure to air once it is chopped, use an additive to speed up the fermentation process, pack it well and cover it in a timely manner. Do all these things and you’ll minimize the window for bad weather to adversely affect your harvest – and you’ll complete the task of making excellent silage.

Mike Bettle
Field Nutritionist
Form-A-Feed TechMix