Silage is a way of conservation providing farmers with very high quality forage, in terms of food value, digestibility and palatability.
Before being cut, grass is composed of about 80% of water. In order to be preserved then stored in the form of hay, water content must be lowered to 15%. For a spring cut with 5T DM /ha, this represents a loss of more than 19T of water per hectare. For spring cuts in May, with the highest productions, this requires several successive sunny days without rain. However, these conditions are not frequent in the spring and do not always occur during the desired period. Improvement of mowing methods and using mowers-conditioners helps accelerate the drying process, but without totally avoiding the exposure to risk. Furthermore, during this long period of exposure, there are losses of dry matter, through the respiration of living cells and the losses of organs, particularly leaves.
One method has therefore been found to preserve the cut grass without requiring on-the-spot drying. The principle of silage is preservation of cut grass in wet form, under anaerobic conditions, lowering the pH which prevents fermentation and thus the decay of the grass.
Freshly cut grass or that which has benefited from few hours of pre-drying is chopped into short blades and placed into a silo where it is packed to expel any air contained in the stock. The silo is then closed airtight. If everything remains wet, the content of dry matter must reach 30% to avoid liquid losses which have a negative environmental impact, generate odours and represent losses of food. In order to avoid the fermentation caused by micro-organisms, the pH must drop very quickly and become acidic. Evolving in an anaerobic medium (oxygen free), lactic bacteria (producing lactic acid) allows the pH to lower up to a value of approximately 4 by transforming sugars from the grass (or corn for example) into acid. Without fermentation, the grass can be preserved.
It is not necessary to dry the grass on site, which allows for greater time flexibility
In terms of volume, wet grass takes up less space than dry grass
All plants cannot be silaged. The fermentation process is prevented if plants have a high sugar content, such as for maize, beetroot, or grasses. Legumes such as Lucerne don’t have such a high sugar content, which complicates their conservation.
The nutritional value of certain plants, especially legumes, is affected by silage, requiring food supplements such as soybean oil cake.
Bacteria found in ensilaged grass can be found in the milk produced by animals, and are sometimes incompatible with the production of derived dairy products (especially cheese).
Silage products can be preserved only one year, as opposed to hay.
In France, 1.4 million hectares are dedicated to the cultivation of corn silage for approximately 16 MT of dry matter (2005).
We estimate that 80% of dairy cows receive ensilaged food.
10 to 15% of forage grass is valued in silage form, that is 2.5 MT of dry matter.
Contamination of silage food by mycotoxins happens on regular basis. Some toxins, such as fusariotoxins (T-2 mycotoxin), are completely independent of storage conditions.