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As I write this during the first days of June, winter is finally behind us, the days have lengthened, and dairy farmers all over New England are planting corn. By the time you read this, the summer will be half over and the corn crop will hopefully be well on its way to maturity and harvest. While a certain percentage is grown for shell corn or high-moisture corn as a substitute for corn grain in dairy diets, the vast majority of the corn crop grown in the dairy regions will be ensiled, stored and fed as forage.
The purpose of ensiling corn is to preserve and store this seasonal crop after harvest. Corn is perfectly suited for ensiling, and when ensiled correctly the majority of the organic matter is preserved with little spoilage. Proper management of the crucial ensiling process will aid in ensuring a high-quality, highly palatable silage that will provide a significant portion of the dry matter needs for the herd.
Once a plant of any kind has been harvested, it immediately begins to decay. This process is driven by the presence of oxygen and bacteria. To keep decomposition (rotting) to a minimum, oxygen must be eliminated from the storage environment. Once the forage is chopped and packed and the air supply is cut off, naturally occurring bacteria ferment the sugars. The key to an optimal fermentation process is eliminating oxygen from the inside of the pile as soon as possible and maintaining proper moisture. If air is allowed to enter or if it takes too long to pack, a pile of forage will continue to heat and destroy the organic matter and nutrients.
As the ensiling process proceeds, acids are produced that stabilize the pile. With corn, lactic acid is the strongest and most abundant one produced; the optimal level is 6 to 8 percent of the total dry matter. Acetic acid is also present in silage, but at lower levels.
During fermentation, much of the acetic acid will be converted to lactic acid. A final lactic to acetic acid ratio of 3-to-1 is desirable. Acetic acid at levels of more than 4 percent of the total dry matter or a lactic/acetic ratio that is inverted indicates a slower fermentation. The more quickly lactic acid can be produced, the less chance there will be for dry matter loss or the formation of harmful organisms such as yeasts and molds.
The presence of higher levels of acetic acid in corn silage is not necessarily a bad thing. What it tells us, however, is that you've probably lost some dry matter due to excessive respiration and the formation of other volatile end products such as alcohol.
The single most critical factor affecting silage quality is the moisture level at the time of harvest, which has repeatedly been shown to have the greatest influence on how well the forage ferments and how much organic matter is recovered. When the moisture level is either too high or too low, conditions are not favorable for adequate lactic acid production, which opens the door for unwelcome acids that affect the stability of the pile and can adversely affect the health of cows.
Butyric and propionic acids are often produced under poor fermentation conditions. Butyric acid can be especially troublesome, since it can be accompanied by high levels of clostridium in the silage. Butyric acid tends to be a greater problem in grass and legume silages. A properly fermented pile of silage should have no butyric or propionic acid.
A properly packed pile of corn silage should have a density of about 45 to 50 pounds per cubic foot. A full analysis of the silage should be done for moisture, fermentation acids, crude protein, soluble protein, neutral detergent fiber, starch, lignin and fiber digestibility. Macrominerals, including potassium, chlorine, sulfur and sodium, should also be analyzed to aid in the formulation of transition cow rations.
Consider using a microbial inoculant on your silage to aid in the fermentation and preservation of the organic matter. Inoculant products contain lactic acid-producing bacteria. Research has shown that the additional organic matter recovery in a pile of silage is well worth the dollars invested in an inoculant. There are a number of dry and liquid inoculants on the market. Consult with your nutritionist or extension agent to determine the best product for your crop.
Mechanical kernel processing has been used on corn crops for many years. A dry stand of corn will benefit the most from a kernel processor. Processing corn silage improves starch and fiber digestion and allows for optimal packing in silos. Be careful about using processors on stands that are too wet, since particle size can end up too small, which will affect rumen function.
The silage storage environment needs to be well-thought-out. Traditionally, upright silos have worked well for smaller herds. Larger herds can make good use of horizontal piles and pits. However, these require more extensive management in terms of covering and protection from weather and the amount of silage exposure as the pile is fed out. Piles should be sized so the face can be removed to a depth of 6 inches or more every day. Leaving part of a pile exposed for several days will negatively impact silage quality.
Dairy farmers have a lot of money invested in a crop of corn by the time it's ready to harvest. Improper harvesting and ensiling will affect the quality and potential for milk production, and there's no way to fix a bad pile of silage once it's been made.
The author is a dairy nutritional consultant and works for Central Connecticut Cooperative Farmers Association in Manchester, Connecticut.