Good quality pasture silage is a good source of energy and protein for a milking cow and can be used as a fibre source when feeding high sugar or starch feeds. However, a poor quality pasture silage (made from low quality pasture, or ensiled with low quality fermentation, or both) will not support high milk yield and will only be suitable for dry cows, or as a fibre source to reduce risk of acidosis.
• Losses when making pasture silage
Losses occur as sugars and protein in the grass is broken down by enzymes and bacteria. This process starts as soon as the grass is cut. Losses decrease quality as well as quantity, because it is the highly digestible components that are most rapidly broken down.
• Losses during harvesting
Losses depend on the dry matter (DM) of the pasture. The optimum DM for silage is 25-30 per cent because total DM loss is minimised.
Cut in the morning of a sunny day, for rapid wilting. Cutting after 1-2 days' sunny weather will result in good sugar levels in the pasture, even when cut in the morning.
Avoid wilting for any more than 24 hours.
Compact the silage well. In a stack or pit, use the heaviest wheeled vehicle available.
Tractor wheels should not sink into the pile of pasture any further than the depth of rubber.
For baled silage make sure that a high-density baler is used.
Seal the stack completely with a weighted, airtight cover. Wash old polythene before use to avoid contamination with the wrong bacteria.
Don't open a covered stack to add more pasture on another day.
Once the silage is sealed, nothing can be done to change the fermentation process. Poor fermentation (e.g. air in the stack) leads to major losses of protein quality. In poorly preserved silage, protein is broken down into ammonia, which decreases the feeding value of the silage. Getting things right while the grass is being harvested will maximise the chance of having a good fermentation:
A fast wilt to 25-30 per cent DM will leave good sugar concentrations in the pasture.
Quick compaction and effective sealing will keep out oxygen, making conditions more suitable for bacteria to convert sugars into lactic acid.
Fast production of lactic acid will quickly reduce the pH, to prevent protein losses.
• Feeding out losses
Silage begins to break down once exposed to air and will begin to heat up as micro-organisms turn the remaining sugars and protein into heat and energy. When feeding out, aim for as little time as possible between exposing the silage to air and the cow eating it.
There are several ways to limit losses from silage while feeding out:
Remove at least 20cm off the whole stack face each day, so silage at the face is not exposed to air for a more than one day.
Cut silage off the face, rather than pulling it off. This keeps a smooth surface at the stack face, which reduces air penetration into the stack.
Leave the stack face open on dry days to avoid heat build-up under the polythene.
Do not feed out more than one day in advance, especially in summer.
Cows will be able to eat more of the silage they are offered if it is fed out on dry paddocks or feed out areas, along fence lines, or in feed bins or troughs.
Do not allow cows access to spoiled silage.
• Why analyse pasture silage?
An analysis will tell you the quality of the silage so you can decide whether to feed milking or dry cows and allows you to value silage based on it Metabolisable Energy (ME) content.
• How to sample silage
Take at least five handfuls of silage from different places and mix them together. Send a subsample of one litre (half a bread bag) for analysis. The sub-sample should be representative of all the silage in the stack or bale.
You can take silage sampled from unopened stack or bales to tell the quality of the feed before it is fed out. (It will also not have been spoiled through exposure to air) or sample silage as it is being fed out.
• Assessing silage quality by sight and smell
If you don't have a feed analysis for your silage, you can estimate quality from its appearance.
High quality silage has lots of leaf, and very little stem. The more stem in silage, the poorer its quality.
Well-preserved silages are green, yellow or pale brown. Dark brown silage is generally poorly preserved.
Well preserved silage has a sweet, tobacco smell. Foul, rancid smells indicate the presence of butyric acid from poor preservation.
Moulds grow where silage has been exposed to air. Some fungi can produce toxins.
