Silage is a type of animal food made from green crops that are cut in the field and
preserved by fermentation for later use. A crop that has been treated this way is said to
have been ensiled (or ensilaged).
Ensiling a sward of mixed grass species allows a farmer to optimise the energy
production, because the grass can be cut at the time of maximum sugar content and
digestibility.
The digestibility of grass is measured in units known as the “D-value” of the grass,
which gives an indication of its digestibility to ruminants. Good quality grazing grass
should have a D-value of about 65D or above.
A large number of different types and varieties of grasses and clovers growing
together is recommended, so that seeding (heading) dates are spread over a longer
period. This ensures that some proportion of the grass crop to be ensiled is at the correct
stage of growth over an extended period.
The types of crops used to make silage are basically the same as for making hay
39–40) to reduce the water content.
Grass is transformed into silage by two main types of bacterial fermentation:
- Carbohydrates in the plant material are converted into organic acids;
- Proteins are converted into aminoacids, which act as preservatives.
Silage that has been properly made is a yellow/brown colour and contains mainly
lactic acid, and some acetic acid, and should have a ph of 4 or less. The best silage is
often made from crops which have been cut after a period of dry, sunny weather, when
the sugar content of the grass is at its highest. The cut grass is normally left for some
hours to wilt ie lose moisture.
Sometimes additives such as molasses are added to increase the proportion of sugars
and formic acid, the latter being useful in increasing the acidity of the silage which
suppresses the growth of harmful Clostridia bacteria. In recent times, many farmers
routinely inoculate their silage (either clamps or big bales) with formulations of freeze-
dried Lactobacillito stabilise the fermentation process.
Food for animals, often referred to as “fodder”, often has to be preserved during or just
after the rainy season, for use in the dry season, or in cold, hard winters, when animal
grazing is limited.
Hay making is a less complicated way to conserve fodder than silage making, and
good hay can be produced with just a sickle, rake and a few days of warm dry weather.
Grass/clover mixtures are the most common form of hay, but it can also be made from:
- millet and other millets, and ryegrass.
- vetches, clovers and field peas.
cereals and grasses such as wheat, oats, Sudan grass, pearl72 TONY WINCH
Monocotyledons -Annual legumes -(1Hg, below); grass/clover mixtures are the most common, and maize is also commonly
used. The plant material should be clean (without soil or faeces), and wilted (1Ef, page