Attention at farm level is turning towards silage harvesting and farmers will be focusing on cutting, wilting and picking up silage. Decisions revolving around these three activities can have major implications for the quality of the resulting silage.

As part of Cut to Clamp, an initiative from Volac which aims to help farmers make consistently better silage, we take a look at the important points to remember when cutting, wilting and picking up your silage.


The feeding value of silage is linked to the amount of leaf and stem present in the sward – an increase in the latter leads to a corresponding fall in quality.

Delaying cutting to boost yields has a negative impact on silage quality, as research shows that the Dry Matter Digestibility (DMD) declines by 2.5-3.0 units for every week delay in harvest between late May and mid-June.

Therefore, it is advisable to monitor the growth of the sward during May and June and to mow just before the seed heads start to emerge.

Another factor that needs to be considered is the sugar content of the grass. Grass sugars are highest on bright sunny days with cool nights.

A high sugar content is important to ensure silage crops preserve properly; if a crop is low in sugar, it can be resolved by wilting or adding an inoculant.

Farmers also need to keep an eye on the weather when planning to mow their silage, as it should only be done when weather conditions allow for harvesting and ensiling to be completed.

Mowing in wet or damp conditions increases the chances of soil contamination occurring, which can result in poor preservation and reduced feed quality.

When it comes to cutting height, it is recommended to mow dense swards to 5cm. But in open swards, this may need to be increased to 7.5-10cm to avoid the risk of soil contamination.

Although dependent on the weather, most farmers will have a rough idea of when they want to mow their silage. Giving your contractor the heads up will make him/her aware that its nearly time to cut and hopefully put you close to the top of his/her list when conditions allow for cutting.


Wilting is an important step when making grass silage as it increases the Dry Matter (DM) percentage and reduces the quantity of effluent produced. Ideally, farmers should aim to wilt their silage to a DM of 28-32% – anything above this will have no benefit on animal performance.

Drying grass, through wilting, makes the sugars more concentrated in the grass, allowing the resulting silage to stabilse at a higher pH. This means that less acid or inoculant is required to preserve the crop.

In ideal conditions, farmers should aim to wilt the grass as quickly as possible to limit sugar losses post-cutting. The problem is, as soon as grass is cut, sugars start declining because they are being used up by the plant, since it is still living, and by undesirable bacteria.

This is important as approximately 6% of the sugars present in grass can be lost during a 24-36 hour wilting period. Therefore, the aim should be to wilt as rapidly as possible to an ideal target DM of 28-32%.

Farmers have two options when it comes to wilting a grass crop for silage.

The first involves wilting the grass rapidly by mowing and harvesting the crop on the same day. For this system, farmers should cut the crop once the dew has lifted and collect it later the same evening.

This method has the potential to increase the amount of sugars present in the grass crop, but only if the weather conditions allow for a rapid wilt.

Or farmers could opt to wilt the crop for 24 hours. Under this method, the crop should be cut in the afternoon when the sugar content of the grass is at its highest.

However, there is a risk of the crop becoming too dry with the longer wilting period, which could have a negative impact on the aerobic stability of the silage at feed-out.

3 things to remember when picking up your silage

Harvesting or picking up the silage crop is important and there are a number of factors farmers need to bear in mind when completing this task. Such factors include: chop length; avoiding field losses; and making sure the entire process runs smoothly.

1. Chop length

Farmers need to avoid the common pitfall of not paying enough attention to chop length, as using the optimum chop length is crucial when harvesting grass.

The optimum chop length has a big impact on how good a consolidation you can ultimately achieve in the clamp or pit.

The ideal chop length is be driven by the DM percentage of the grass and, generally speaking, the drier it becomes the shorter the chop length that is required.

Gannon silage

As a guide, if the grass is >30% DM, chop to 1.5-2.5cm to help improve consolidation.

But if it’s highly-digestible grass, the chop length may need to be increased to 5cm to ensure that there is sufficient effective fibre in the diet of the animal consuming the silage.

If grass is at 20-30% DM, farmers should use a chop length of 2.5-5.0cm and if it’s <20% DM you may need to increase the chop length up to 10cm to reduce effluent and prevent clamp slippage.

2. Limit field losses

Irish farmers and contractors often face a battle with the weather when picking up silage crops and the risk of rain may force some to overfill trailers.

However, overfilling trailers can result in losses and doing so can result in 1-2% of the grass crop being lost in the field. It may not seem like a lot, but on large acreages it can amount to a substantial amount of potential feed.

3. Sharp knives and delays at pitting

Both farmers and contractors also need to ensure that knives on silage wagons and harvesters are sharp to ensure an even flow of material through the machine.

Keeping the knives sharp and making necessary adjustments, if needed, can have a positive impact on the amount of fuel used during the harvesting stage.

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 preserves nutrients.

However, an efficient fermentation requires air-free conditions within the clamp (pit).

Therefore, making sure the path to the pit is clear is important. A five-minute delay in the yard on 10 loads of silage could be the difference in covering the pit in the light of day or in darkness.

This post is sponsored by Volac as part of its Cut to Clamp initiative, which aims to raise the profile of good silage as a vital part of modern farming. Click here for more information on the Cut to Clamp initiative