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A fodder made from grass, maize, or other leafy material and preserved by its own partial fermentation in an airtight tower-silo, silage pit or, more commonly, in a large airtight roll baled and sealed in plastic sheeting. Silages are usually made for the winter housing period for stock and to allow excess grass growth in the spring and summer to be preserved. Initial fermentation creates organic and amino acids, which act as preservatives. Silage is fed mainly to beef and dairy cattle, but can be fed to other ruminants. An average grass silage has feed value of 10·2 MJ/kg of metabolized energy, a D value of 64, crude protein content of 14% in dry matter, and a digestible crude protein of 95 g/kg. Among the advantages of silo making over hay is that it is not dependent on dry weather and may therefore be harvested at its best feed value. It is not labour-intensive, and it allows the farmer to provide feed for his livestock away from the farm if required.

Portions of the summary below have been contributed by Wikipedia.

Silage is fermented, high-moisture forage to be fed to ruminants, cud-chewing animals like cattle and sheep. Silage is most often made from grass crops, including corn (maize) or sorghum.

Silage can also be made from many other field crops, and other names (oatlage for oats, haylage for alfalfa) are sometimes used when this is done.

Silage must be made from plant material with a suitable moisture content, which ranges from about 55% to 70% depending on the construction of the storage structure and hence the degree of compression and the amount of water that will be lost during storage. In New Zealand and Northern Europe it is harvested directly from the paddock by a tractor-mounted silage chopper, blown into a trailer-mounted cage and transported to the silo or heap.

In the US, the plant material is collected, chopped into pieces about 1/2″ (13 mm) long and packed into the storage. In the early days of mechanized agriculture, cornstalks were cut and collected manually using a knife and horsedrawn wagon, and fed into a stationary machine called a “silo filler” that would chop the stalks and blow them up a narrow tube to the top of a tower silo. Harvesters blow the silage into the wagon via a chute at the rear or side of the machine. For tower silos, the silage is emptied into a stationary blower which blows the silage up into the silo. Silage may also be emptied into a bagger, which puts the silage into a large plastic bag that is laid out on the ground.

In Australia silage is left in big heaps on the ground and is rolled by large tractors to push all the air out then covered in large plastic covers which are held tight on the heap by recycled tyres.

In New Zealand and Northern Europe the silo or ‘pit’ is often a concrete bunker built on the side of a bank so that chopped grass can be dumped in at the top and fed out from the bottom in winter.

Silage undergoes anaerobic fermentation, typically beginning about 48 hours after the silo is filled. today, some silage is inoculated with specific microorganisms to speed the fermentation or to improve the resulting silage.

The fermentation process releases a liquid.

Silage must be protected from oxygen or it will spoil. Silage must be firmly packed to minimize the amount of air present.

Silos are hazardous, and people die every year in the process of filling and maintaining them. The machinery used is dangerous, and with tower silos workers can fall from the silo’s ladder or work platform. The reduced oxygen environment inside the silo can cause asphyxiation, and molds formed when air is allowed to reach cured silage can cause toxic organic dust syndrome.

The ensiled product retains a great deal of the nutrients present in the plant, much more so than if the crop were dried and stored as hay or stover. Silage is most often fed to dairy cattle, because they respond well to highly nutritious diets.

Since silage goes through a fermentation process, energy is used by fermentative bacteria to produce volatile fatty acids (VFA), such as acetate, propionate, lactate, butyrate etc, which preserve the forage. The end result is that the silage, is lower in energy than the original forage, since the fermentative bacteria use some of the carbohydrate present in the fresh material to produce VFA.