SILAGE

'Silage is an essential element of effective feeding on our farm - but what is it and what makes it so useful?'

Silage is simply fermented fodder stored in an airtight condition (in a pit or bales) to be fed to livestock in winter or when grass growth is poor due to drought or very wet conditions.

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The grasses are cut and then fermented to keep as much of the nutrients (such as sugars and proteins) as possible. The fermentation is carried out by microscopic organisms living in the grass. The process must be carried out under acidic conditions (around pH 4-5) in order to keep nutrients and provide a form of food that cows will like to eat. Fermentation at higher pH results in silage that has a bad taste, and lower amounts of sugars and proteins leading to reduced intakes.

MAKING SILAGE

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First, the pasture must be cut when the grasses contain their highest nutrient levels. This is usually in spring just before the grass is fully mature and goes to seed. This is important because all forms of preserved grass, such as hay and silage, will have lower amounts of nutrients than fresh pasture, so everything must be done to make the end product be as nutritious as possible.

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Grass is allowed to wilt in the field for twelve hours after mowing to reduce the moisture content to around 60-75%. This moisture level will allow for optimum fermentation. If the grass is left out longer it may get too dry or it may get rained on, either will have a negative impact on proper fermentation. Also, the longer the grass is left uncut, the higher the loss of nutrients.

FERMENTATION

The cut grass is chopped into even smaller pieces and then compacted to get out as much oxygen as possible (this is important because the microorganisms, called lactic acid bacteria, that are needed to carry out the fermentation like living in oxygen-free environments). Removing and keeping out oxygen is a key part of making silage. This is because fermentation has to happen under anaerobic (oxygen-free) conditions, or the correct type of microorganisms won’t grow.

While oxygen remains, plant enzymes and other bacteria and microorganisms react with the plant sugars and proteins to make energy, reducing the amounts of these nutrients in the grass. Once all of the oxygen is used up, lactic acid bacteria start to multiply. These are bacteria that are needed to make the silage, and they turn the plant sugars into lactic acid. This causes the pH to drop (the mixture because more acidic). Once the pH is around 4-5, the sugars stop breaking down and the grass is preserved until the silage is opened and exposed to oxygen.

If the pH isn’t low enough, a different kind of bacteria will start fermenting the silage, producing by-products like ammonia that taste bad to animals.

THE SILAGE PIT

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If the silage is to be stored in a pit, a tractor or other machine is driven over the grass pile until it is firm and all air pockets are filled. If the silage is stored as bales, the baling machine will compact the grass as it works.

The next step is to seal the compacted grass with plastic to keep oxygen out. Mounds of silage are covered with large polythene (plastic) sheets and weighted down (usually with rubber mats or old tyres) to ensure maximum compacting; bales are covered with a plastic wrapping.

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THE PROBLEM WITH OXYGEN

Removing and keeping out oxygen is a key part of making silage. This is because fermentation has to happen under anaerobic (oxygen-free) conditions, or the correct type of microorganisms won’t grow.

While oxygen remains, plant enzymes and other bacteria and microorganisms react with the plant sugars and proteins to make energy, reducing the amounts of these nutrients in the grass.

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Once all of the oxygen is used up, lactic acid bacteria start to multiply. These are bacteria that are needed to make the silage, and they turn the plant sugars into lactic acid. This causes the pH to drop (the mixture becomes more acidic). Once the pH is around 4-5, the sugars stop breaking down and the grass is preserved until the silage is opened and exposed to oxygen.

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If the pH isn’t low enough, a different kind of bacteria will start fermenting the silage, producing by-products (like ammonia) that taste bad to cows.