An Introduction to Silage

Silage is feed that has been preserved by acidification - the result of fermentation in the absence of oxygen. Any green crop with adequate water-soluble carbohydrates (sugars) and the correct moisture content can be cut, chopped and ensiled.

Suitable crops include corn and other cereals, legumes such as faba beans and alfalfa, perennial grasses and even weeds such as kochia. The most popular silage crops in Manitoba are cereal grains, corn and alfalfa.

Ensiling Process

The green crop is cut and chopped, placed in a silo, packed and covered or sealed as quickly as possible. Then, biochemical processes transform the crop into silage.

Within the first few hours, an aerobic reaction begins which consumes all of the oxygen in the silage. The duration of this reaction may range from a few hours to several days. Heat is created and valuable nutrients are consumed during the reaction. It is important to manage the forage properly beforehand to minimize the length of this process.

Once all the oxygen has been consumed, fermentation begins, producing lactic acid which lowers the pH (acidity) level in the feed. When the pH level drops to a certain level, usually within three or four weeks, fermentation stops. The silage is ready.

Pros and Cons


  • Silage can be harvested in almost any weather conditions.
  • Lower dry matter loss during harvesting means higher outputs of nutrients per acre.
  • Permits the use of a wider range of crops than other forage systems.
  • Can salvage crops damaged by hail, frost and high weed content.
  • Large quantities of uniform quality feed can be stored.
  • Palatability can sometimes be improved in crops such as sweet clover.
  • Handling is mechanized from the field to feed trough.


  • Requires more labour and time than hay.
  • Has an odor that may be offensive if stored near populated areas.
  • Capital investment required for storage facilities, forage harvester.
  • Has limited market potential. Long distance transportation is inefficient because silage is heavy and deteriorates with exposure to air.

Types of Silos

The most common types of silage storage in Manitoba are:

  • round bale silage
  • horizontal (bunker) silos
  • vertical silos (concrete stave, oxygen limiting)

Factors Affecting Good Silage

Cover it Quickly

Silage spoils when exposed to the air - plain and simple. It's important to fill the silo rapidly, pack it well and cover it as soon as possible. When a sealed silo is opened, the fermentation process can begin again. Spoilage is minimized in silos that have been filled rapidly, packed well and sealed quickly.

The key to producing good silage lies in controlling the fermentation process. "The quicker, the better" is the rule of thumb when it comes to fermentation because nutrients from the feed are consumed in the process.

Although some biological and chemical factors are largely outside of the producer's control, there are others the producer can manage to optimize silage quality.  


Moisture content of the crop at harvest is likely the most important factor in determining silage quality. If the moisture is too high, the fermentation process may not stabilize, resulting in nutrient loss and spoilage. Wet silage may also freeze, creating handling difficulties.

If the moisture content is too low, the silage will not pack well. Loosely-packed silage holds a larger amount of air which feeds the aerobic process, resulting in excess spoilage. Higher leaf loss will occur when harvesting drier crops, lowering the protein content.

Harvest at about 65 per cent moisture for most silos:

  • cereals at about three weeks after heading-out, or at, or slightly before, early dough stage;
  • corn at the hard dough stage;
  • peas, lentils and faba beans just when the pods have begun to wrinkle;
  • alfalfa when in early to full bloom.

Less mature crops may be higher in protein, but the overall volume of dry matter will be less.

The desirable moisture content for making round bale silage is 50 to 60 per cent.  

Particle Size

Chopping, cutting and bruising all improve the potential for making good silage because these processes improve packing and encourage bacterial growth. A theoretical length of cut (TLC) of one-quarter to one-half inch is recommended, depending on the crop.

Take note that smaller chopping requires more power and may slow the harvest.  

Water-soluble Carbohydrate Content

The fermentation process is fueled by water-soluble carbohydrates (WSCs), or sugars. In general, the higher the level of WSCs, the better the fermentation.

All plants contain WSCs - some more than others. Legumes are generally lower in WSCs than cereals and grasses, making them more difficult to ensile.  

Buffering Capacity

The pH level must be lowered as quickly as possible to ensure good preservation. Some plants, such as legumes, are "well-buffered" and resist this change more vigorously than others. Valuable nutrients are burned up during the extended process of lowering the pH in resistant plants.