Step 3. Harvesting
Avoid the common pitfall of not paying enough attention to chop length.
Using the optimum chop length is crucial when harvesting grass, because it has a big impact on how good a consolidation you can ultimately achieve in the clamp.
Silage is produced when beneficial bacteria ferment some of the sugars in grass to lactic acid. This ‘pickles’ the grass, preventing the growth of spoilage micro-organisms and so preserving nutrients. However, fermentation only starts once there is no air left in the clamp. So the quicker you can achieve this, the better.
TOP TIP: Ensure knives are kept sharp and adjusted.
Too long a chop makes it more difficult to squeeze all the air out of the spaces between the grass, particularly at higher dry matters. But too short a chop can also cause problems. So as well as keeping knives sharp, ensure they are correctly adjusted according to the crop’s % dry matter.
As a guide, if grass is > 30% DM, chop to 1.5-2.5 cm chop length to improve consolidation (though if grass silage is being fed as part of a high maize diet, chop length should be increased to ensure sufficient effective fibre in the complete diet).
If grass is at 20-30% DM, use a chop length of 2.5-5.0 cm.
If grass is <20% DM, you may need to increase up to 10cm to reduce effluent and prevent clamp slippage.
Multi-cut hints and tips
Although cutting grass younger has the benefit of it being more digestible (and providing more metabolisable energy), the slight downside is that it's lower in fibre.
Which means it can be more prone to slipping in the clamp.
As a result, chop length at harvesting may need to be longer when making multi-cut than when cutting older grass crops.
As an example, for a 75 D value silage at 30% DM, consider a 5cm chop length to help hold it in the clamp.
This can also help it stay in the rumen slightly longer, allowing the cow to extract better nutritional value.
Volac and Germinal have developed a 10-point multi-cut grass silage checklist, designed to help you get the most from your grass silage making process.