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Silages: Quality equals money

John Hibma Published on 20 July 2010
silage harvest

Ensiling forages – usually cereal, grasses or legume crops – is a very practical and cost-effective way for dairy farms to preserve and store feeds. Even though the process of ensiling has been utilized for many centuries, and modern research abounds on the proper ways to ensile forages, it’s amazing how many dairy farmers carelessly or ignorantly wreck a crop of corn or haylage through an improper ensiling process.

Especially in these days when our industry finds itself struggling with low milk prices, high-quality, fermented forages can help a dairy farm make it through the tough economic times.



Whether a dairy farmer makes the investment in growing and harvesting the crop or purchases it standing in the field, the crop constitutes a sizable investment. If quality is lacking, it will, most assuredly, have a negative affect on the financial bottom line. (And bad silage can’t be sent back to the manufacturer.)

Ensiling your forages is all about preserving and recovering as much dry matter and plant nutrients as possible. The most critical factor affecting silage quality is the moisture level of the forage at the time of harvest and packing. Trials have shown repeatedly that the moisture level at the time of harvesting of both corn silage and haylage has the greatest influence on a good fermentation and how much dry matter can be expected to be recovered.

The ensiling process is accomplished through a fermentation process that results in the formation of several different acids that are produced by various bacteria present in the environment. The end products of the fermentation process are acids that stabilize the plant material. A properly fermented pile of silage should use up all the air very quickly (in a matter of a few days), produce a lot of lactic acid and stabilize with a pH of about 4. The more rapidly this occurs and the more lactic acid produced, the better quality silage you will have.

The goal of the ensiling process is to get through the respiration process as quickly as possible as the anaerobic fermentation takes over. The predominant silage acids produced during the fermentation process should be lactic and acetic acid. A silage that has any levels of propionic or butyric acid was not harvested or put up properly. Lactic acid is the strongest of the silage acids, and the presence of higher levels of lactic acid indicates that the fermentation process has progressed rapidly, which should result in a well-preserved and stable silage.

A carelessly managed pile of silage doesn’t necessarily affect only the milk cows. A number of years ago a client of mine in California had done a poor job of putting up a bunker of alfalfa haylage. The sides of the pile up against the cement walls of the bunker had not been packed well and the alfalfa had continued to heat, making about half of the original crude protein useless due to heat damage. Knowing that the silage was damaged, this dairy farmer chose to feed the haylage on the sides of the bunk to his young heifers, thinking that it wouldn’t “hurt” them. After I’d begun doing the nutrition work for his milking herd, he said to me one day, “John, my heifers aren’t growing as fast as they should. What do you think might be wrong?”


Once a plant has been harvested, it immediately begins to decay. This decaying process is driven initially by the presence of oxygen. To keep heating and decomposition (rotting) to a minimum, oxygen must be eliminated from the environment. We do this, of course, by stacking the feed on a big pile and squashing it down with a tractor. Or we pack it horizontally with a bagger, or we use the silage’s own weight to pack itself if put up in an upright silo.

In addition, the longer the fresh-cut feed is exposed to air and oxygen, bacteria that are more favorable to acetic acid production will thrive, reducing the amount of lactic acid fermentation. While acetic acid is not harmful, its excessive presence indicates a slower fermentation, excessive respiration and the disappearance of dry matter in the form of ammonia and alcohol. In all cases, the oxygen in the pile must be used up as quickly as possible with no more being allowed to penetrate the pile. As the air is being eliminated, bacteria that are present in the feed begin a predictable process of fermentation.

Over the past several decades, commercial products called silage preservatives or silage inoculants have become very popular in aiding the rapid fermentation in silage piles. These products supply strains of bacteria that will increase the production of lactic acid in the silage. Haylages, in particular, will benefit from inoculants due to the difficulty often encountered with packing and moisture levels. Poorly ensiled haylages are very prone to butyric acid production, which, besides being very smelly and unpalatable, can be toxic to animals if the levels are high enough.

So how did your silages turn out last year? Did you chop your corn at the right stage of maturity and moisture? Did the grain still have some milk in it or was it into a hard dent? Did you allow the grass to wilt a little before chopping? Was it as high as the top of your pickup truck when you got around to chopping it? If you packed your silage into a bunk did you get it packed down quickly enough and with enough weight to squeeze out all the air? Did the pile get covered and sealed within a day of chopping? How many days did it take you to get your 20 acres chopped and covered? Did you use a preservative to help with fermentation?

For many dairy farms, high-quality corn silage supplies a significant portion of dietary energy in feed rations. Except for the highest production groups, corn silage represents the best value of energy on a per-unit basis. Even though haylages can be a challenge to make, done right they can help offset protein costs in feed rations for milk cows as well as heifers. Work with your nutritionist or feed company professional in growing, harvesting and incorporating high-quality silages into your feeding programs. PD

John Hibma is a freelance writer from South Windsor, Connecticut.


PHOTO : Once a plant has been harvested it immediately begins to decay. Photo by PD staff.

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