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Guide to basic silage principles for new employees

Bill Braman Published on 06 February 2014

What is silage?

Crops such as corn, alfalfa and grass are preserved and stored as silage. Silage inoculants work with the lactic acid found naturally in crops to ferment sugars into lactic and other acids and alcohol to lower pH levels to preserve the crop for later feeding.

Acids also provide energy to animals. Four elements are key to silage quality: the right amount of moisture, plant sugars and lactic acid bacteria (LAB), as well as oxygen-free conditions.



An example of lactic acid fermentation is the conversion of cabbage to sauerkraut for preservation for later use. The sour taste is the lactic acid. Pickling cucumbers and the production of yogurt are other examples of preserving foods by lactic acid fermentation.

Four phases of silage production

PHASE 1: Aerobic

After whole plants are cut and harvested, plant cells continue to “breathe.” This continues even as the forage is ensiled until all the oxygen is gone. Oxygen is your “enemy” and needs to be eliminated fast to prevent aerobic, or oxygen-loving, bacteria and other micro-organisms like yeasts and mold, from growing. Heating at temperatures 15 degrees above surrounding temperatures is a sign that the aerobic phase is persisting too long.

A backyard compost pile is an example of an aerobic fermentation, which decreases dry matter, producing heat while breaking down the carbohydrates and proteins – opposite of good silage fermentation.

PHASE 2: Anaerobic

This stage begins when all oxygen is depleted. Anaerobic lactic acid bacteria start the fermentation process, converting plant sugars into lactic acid, among other things. Lactic acid lowers the silage pH faster.

A continuous decline in pH inhibits undesirable micro-organisms; pH levels in whole corn should drop below 5 in less than 24 hours and in less than 72 to 96 hours in alfalfa. If pH levels remain high, there is higher dry matter loss and greater yeast and mold growth. Lactic acid reduces the loss of nutrients and is a vital source of energy to cattle.


Phase 2 stops when the pH is low enough to inhibit bacterial growth. If forage is properly ensiled and inoculated with lactic acid bacteria, fermentation is typically complete in two weeks.

Many types of bacteria are found naturally in crops, but there may not be enough “good” bacteria for optimal fermentation. Applying bacterial silage inoculants containing specific lactic acid bacteria (LAB) during harvest helps ensure rapid and uniform fermentation.

Why lactic acid is important

Fermentation that produces lactic and acetic acids plus alcohol can generate up to a 24 percent loss of dry matter. In comparison, LAB can convert forage sugars into only lactic acid, which eliminates dry matter (energy) loss – and the loss of feed. Guidelines for volatile fatty acid and fermentation compounds for corn silage are shown in Table 1.

0314pd_braman_Guidelines for volatile fatty acid and fermentation compounds for corn silage_1

PHASE 3: Stable

Once LAB growth stops and the silage reaches a terminal pH, the stable phase begins. If the silo is properly sealed, there will be little microbial activity and minimal nutritional loss. “Oxygen is your enemy.”

PHASE 4: Feedout

Oxygen invades the silo face (surface) when feedout begins and continues until it is used. Yeasts and molds that were dormant grow and cause aerobic deterioration. This heats up the silage and causes excessive loss of dry matter and nutrients. Fermenting yeast and simple sugars from corn or barley with oxygen present to produce alcohol (for example, beer) is an example of a loss of dry matter, but it tastes good.


Losses during silage production

Field losses are associated with field-wilted forages. Cell respiration will continue until forage reaches 40 percent moisture. Respiration dry matter losses (can range from 2 to 8 percent) occur with the breakdown of nutrients by plant enzymes, aerobic yeasts and molds while the crop is exposed to oxygen.

Over-wilting will result in excessive field loss of nutrients, difficult packing and poorer fermentation in the silo. To minimize field losses, harvest at the proper stage of maturity, moisture content, chop length and during weather conditions favorable to wilting. The faster the silo is filled, the lower the respiration losses.

Clostridia bacteria grow in low (less than 30 percent) dry matter legume forages. They are present in the soil and introduced to forage during harvest. Clostridia breaks down proteins, organic acids and sugars into butyric acid, ammonia and carbon dioxide that cause dry matter loss.

Ammonia and butyric acid raise the silage pH and make silage unpalatable to cattle. To prevent contamination, wilt forage to at least 35 percent dry matter and avoid disrupting the soil surface during harvest. Silage inoculants with active LAB strains inhibit clostridium fermentation; some LAB strains inhibit clostridium growth.

When the silo is opened during feedout, oxygen exposure leads to aerobic deterioration and dry matter loss. As silage temperatures rise three degrees above ambient temperatures, yeast, molds and other micro-organisms convert sugars and organic acids to carbon dioxide, or heat and water that spoil feed.

To prevent spoilage, feed out at least 6 inches a day from the silo surface. Remove more during the summer when temperatures are high. A smooth face and feeding from across the entire exposed surface each day reduces aerobic spoilage.

What dry matter losses should I expect during ensiling?

You can expect anywhere from 8 to 25-plus percent. Poor harvest moisture levels, packing, silo covering and feedout management techniques can all lead to dry matter losses of 25 percent or more. With corn silage costs of $60 per ton, this represents $15,000 per 1,000 tons of whole-corn crop forage.

Studies show that proper management, plus the right LAB silage inoculant, can reduce losses by as much as 8 percent or $480 per 1,000 tons of fresh-corn crop forage.

Why is packing critical?

Proper packing protects the silo from oxygen and decreases aerobic activity. A good rule for packing is 800 pounds of packing tractor weight to every 1 ton of forage added per hour. You need 80,000 pounds of packing tractor for a filling rate of 100 tons per hour (800 x 100).

Measure silage density by taking core samples to determine packing effectiveness; 15 pounds of dry matter per cubic foot is minimum, and best practice exceeds 20 pounds of dry matter per cubic foot.

Why cover immediately?

“Oxygen is your enemy.” Once the silo is packed properly, it should be covered and sealed with heavy plastic or a cover designed for silage, and then covered with tires. This minimizes the silo’s exposure to oxygen and inhibits the growth of aerobic micro-organisms.

Tires are placed over the cover for a tight seal. They should touch each other for optimum effect. If holes develop in the cover, patch immediately to prevent oxygen penetration.

Why is silage corn kernel processing necessary?

As a corn plant matures, the grain deposits a starch-protein matrix that is hard to digest. To increase starch digestibility, corn kernels can be smashed with a kernel processor on the silage chopper. Laboratory methods are available to measure corn kernel processing effectiveness and are useful management tools during harvesting.

When should I use a bacterial silage inoculant?

Always. Like car or house insurance, they protect against potential losses. Studies show that fermentation improvement occurs two-thirds of the time with haycrop silage, and 40 percent of the time with corn silage. Given these odds, an inoculant is good “insurance” against “bad” bacteria that result in high dry matter losses, lower feed value and suboptimal animal performance.

What is the ideal application rate?

It is not the quantity of bacteria. What is important is the number of live (emphasis on “live”) LAB added. A minimum of 90 billion LAB per ton of fresh forage, or 100,000 CFU per g of forage is best.

Liquid or dry inoculants?

Dry and liquid applications are available, but liquid applications have several advantages. Liquid inoculants ensure more even distribution. Dry products can separate. Liquid products start growing immediately as they come in contact with forage sugar.

Dry inoculants need bacteria to be moistened with plant juices before they grow. Another advantage of liquid inoculants is that they usually cost less per ton of treated forage than dry applications for the same number of live bacteria. PD

Bill Bramanis director of innovations withCHR Hansen. Email Bill Braman.