Grass silage is a way for farmers to keep their cows and sheep fed during times when natural pasture isn’t as good, such as in the dry season. It’s made from grasses that have been ‘pickled’ by bacteria to prevent spoilage microorganisms growing and destroying the nutrients in the grass.
Making silage takes a lot of work, but it’s also a great way to make extra income for your farm. It’s cheaper to make than buying hay or lucerne, and it can be stored longer. It’s also more nutritious, because it’s made from grass that has a higher level of vitamins and minerals than fresh pasture, and contains more fibre.
The process of making grass silage starts when you cut your grass into swaths and then use a mower to chop it into small pieces. This reduces the amount of air in the grass, so fermentation can start. This is done by using bacteria that live in the grass called lactic acid bacteria. These bacteria break down the plant sugars in the grass and produce lactic acid, which lowers the pH of the mixture (this means it’s more acidic). Once the silage has a pH of around 4-5, the sugars are broken down and the forage can’t spoil.
Once the grass has been chopped into small pieces, it’s stacked up in a pile to remove as much air as possible. It’s then covered with huge polythene sheets and weighted down (usually with old tyres) to ensure it compacts properly.
Keeping out oxygen is a very important part of the whole process, because it’s vital that lactic acid bacteria can grow in an oxygen-free environment. When the bacteria have used up all the oxygen, they start fermenting the plant sugars into lactic acid. This lowers the pH of the mixture and keeps it safe until it’s opened and exposed to oxygen. If the pH isn’t low enough, another type of bacteria can start to ferment it and produce by-products that taste bad to cows and sheep.
This is why it’s crucial to get the chop length right. A shorter chop length will cause more air to escape from the grass, which will make it harder for the lactic acid bacteria to do their job. It will also increase the risk of Clostridia contamination, because the bacteria won’t have as many oxygen-rich areas to multiply in.
It’s also vital to keep the pile as compacted as possible, so it doesn’t wilt too quickly and cause mould. This is why it’s important to use a mower that’s designed for preserving grass and has a high-powered cutter blade. It can take several hours to get the chop length to the correct size, so be sure to do this in a sunny spell of weather.
The next step is to seal the compacted grass in a plastic covering and store it for later. This can be done either as mounds, which are covered with large polythene sheets and weighted with tyres, or in bales, which are wrapped in plastic film. This protects the grass from water and pests like birds and rodents, but it can also help it last longer in storage. The plastic should be thick and strong, as well as breathable to prevent mould growth.