What is silage and how is it made?

What is silage?

Sometimes referred to as ensilage or pickled forage, silage is a type of livestock feed that is comprised of forage plants like legumes, corn, wheat, or other cereal grasses that have been finely chopped and stored in such a way that they ferment, a process that acidifies theses plant to preserve essential vitamins and nutrients. Silage is often used to feed cattle, sheep, goats or other ruminants.

How is it made?

To make silage, farmers must cut and harvest the forage for this process when the forage contains the highest level of nutrients possible, generally just before the plants are fully mature. Because fermentation results in the breakdown or loss of some nutrients, timing the forage harvest is essential to ensure that the resulting silage retains the desired nutrients. As with other preserved forage, silage is not as nutritious as fresh grass, although it is preferred by many farmers because it retains more vitamins and minerals than dried forages, like hay.

Once cut, the forage is left in the field for several hours in order to wilt, a process in which water is lost from the plant. Once the moisture content of the forage is approximately 60-75%, the optimal moisture level for fermentation, the cut forage will be gathered for further processing. To ensure proper moisture content, cut forage should not be allowed to dry too thoroughly, a process that can lead to hay, or to be rained on, as this can cause the cut forage to reabsorb unwanted moisture.

This slightly dried forage is then chopped into small pieces and compacted. The compaction process is also essential to successful silage-making, as this process aids in the removal of oxygen from the forage materials. Fermentation, or the pickling process that preserves the forage and renders it safe for future consumption, can only happen under anaerobic, or oxygen-free, conditions. Therefore, if oxygen levels remain too high in the silage, it can lead to the growth of bacteria or other microorganisms that can react with naturally occurring plant sugars and proteins, thus reducing the nutrient levels in the silage.

Upon the removal of oxygen from the processed forage, lactic acid bacteria then begin to consume plant sugars and produce the lactic acid necessary to ferment the silage. As these bacteria multiply, the resulting lactic acid concentration causes the mixture to become more acidic, lowering the pH level of the silage. Once the proper pH is reached, typically between 4-5, the sugars in the plant material can no longer break down and the forage is preserved. The silage is then stored in and will remain preserved until exposed to oxygen; once this exposure occurs, the fermentation process is halted and the silage begins to break down and lose nutrients.

Silage Storage
Once harvested and chopped, silage must be stored in an environment that can remain anaerobic or sealed against oxygen. In many instances, silage is stored in tall, upright structures called silos for fermentation; hence the name, silage. However, only large farming operations typically employ silos for silage storage; smaller farms may utilize storage pits, mounds or bales. When utilizing storage pits, silage is piled into a large pit, and then covered and compacted by tractors or other large machines until the forage in the pit is firm. If baled, the silages will be compacted by a baling machine, and both bales and mounds of silage will be covered with large plastic sheets and weighted to ensure that the mounds and bales are protected from the elements and kept as oxygen-free as possible. Regardless of the method of storage, it essential that the silage remain in an aerobic state in order for correct fermentation to take place.