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The key to producing top-quality silage

Over the years the Agri-Food and Biosciences Institute has analysed thousands of silage samples.

Lots of advice and articles have been written on the topic but the common theme that has emerged is that while the dry matter content of silage increased over this time, in general, there was little improvement in its nutritional quality.

So, why is that the case?

Kevin McGrath, a Beef and Sheep Adviser at the College of Agriculture, Food and Rural Enterprise (CAFRE) said: “Making good quality silage can be a difficult task. We have changeable weather and so we have short windows of operation for the silage contractors.”

“But the biggest issue can be our need for bulk at the expense of quality. By delaying harvest to achieve bulk, yields are increased but quality declines.”

“Most Beef and Sheep farms will have a mixture of stock each with different feed demands. Common practice on many beef and sheep farms is to produce a large crop of silage of low to average quality, making up the nutritional shortfall with expensive concentrates.”

“With tight margins and the fact that stock are housed for up to six months of the year, we need to focus on improving our silage quality to increase output and reduce costs.”


The next question, therefore, becomes where do we start the process of increasing yield at a lower price?

Kevin McGrath added: “Growing grass, whether for grazing or silage, needs the correct nutrition. Soils must be analysed with appropriate levels of Lime, Nitrogen, Phosphate, Potassium and Sulphur applied depending on results.”

“A grass plant suffering nutritional stress will naturally grow to head to reproduce, compromising both quality and quantity.”

“You must apply fertiliser at the correct time. This means formulating a nutrient management plan based on soil analysis results. Apply slurry when grass cover is low to avoid the risk of contamination and poor fermentation.

“Nitrogen fertiliser should be applied at no more than 120kg/ha first cut, 100kg/ha at the second cut and 80kg/ha third cut. Sulphur isn’t stored in the soil. It will raise both sugar and protein levels which can improve both fermentation and production.”

“Weeds reduce silage quality, can cause dietary upset and are more difficult to ensile. Docks, for example, are 65 per cent of the nutritional value of grass. At a 10 per cent sward presence, this is the equivalent of 1 silage bale/10 of docks. Spray 3 – 4 weeks before harvest.”

“You should also consider reseeding as ryegrasses have higher digestibility with improved yields over poorer swards. Due to a higher sugar content, fermentation and preservation will also be better.”

“Late heading ryegrass varieties can be harvested eight days later than Intermediate varieties with similar yield and ensilability but with higher digestibility.”

“A clean sward in March is essential for quality silage. Graze tightly with young stock or sheep in the autumn. Silage quality will be reduced if the yellow-dead material at the base is not grazed off. Grazing once in spring can reduce first cut yield but silage quality is decreased accordingly.”

Cutting date influence

The harvesting process will be aided by the fact that the grass cutting date has the greatest influence on silage quality.

An earlier cut of higher quality grass may allow reduced concentrate use but first priority is to ensure an adequate supply of silage to feed all stock over the winter period. When quantity is available the focus must change to optimising quality.

Digestibility, measured in D-value, falls by 0.5 D-value a day from the grass plants start to develop flowering stems. Target D value depends on the class of stock to be fed. 67 D is the minimum target for productive stock and coincides with 50 per cent ear emergence.”

“Remember each week delay in cutting could require an extra 1kg of concentrate/weanling/day or 0.25kg /lamb/day to compensate for loss of silage quality.

“As a rule of thumb, one day’s growth should be allocated for each 2.5kg of N applied. A failure to utilise all the nitrogen can lead to poor fermentation. This has led to farmers delaying harvesting especially if fertiliser has been applied late.

“Pre-cut testing is available indicating both nitrate and sugar levels. If there are risks of residual nitrates at cutting, wilt grass to 30% dry matter using a quick wilt to reduce the loss of sugars ensuring a good fermentation,” Kevin added.

Ideally farmers should aim to wilt their grass quickly to 25 to 30 per cent dry matter. Wilt for 24 hours to increase the concentration of sugars in the grass which in turn improves fermentation and intakes. And, also be aware that longer wilts can lead to digestibility losses, consolidation issues and feeding out losses.

It isn’t always possible but try to cut grass and lift grass in the late afternoon. This avoids the dew whilst also ensuring sugars are at their highest.

Chop length is also an important consideration as it affects consolidation in the pit, clamp or bale. The dryer the grass the shorter the chop length should become. For a DM of 25 – 30 per cent aim for a chop length of 2.5 – 5cm.

For a wetter crop of grass of less than 22 per cent DM, aim for a chop length of 10cm. Chopped silages break down more rapidly in the rumen but too short can also lead to poor rumen health.

Highly digestible grass should have a chop length of 5cm minimum to ensure sufficient fibre in the diet.


Cut dense swards to a recommended cutting height of 5cm with more open swards increased up to 10cm. This avoids the risk of soil contamination occurring. Soil contamination can cause a poor fermentation, reduce the feed value while also increasing the risk of listeria.

Raking and mowing are the two main risk areas of contamination at harvest. Remember, swards cut too low also take longer to recover.

Fill the clamp/pit as quickly as possible. It is important to spread the grass evenly and not to fill in deep layers. Roll the pit constantly when filling. A good buck raking technique is important as a heavy tractor is only effective at expelling air down to a 20cm depth.

Once the pit is filled, do not roll the following day as this can allow air to re-enter and affect the fermentation process. If possible, cover the grass each night during the filling process to avoid losses.

Kevin McGrath commented: “We can’t forget baled silage as it offers flexibility and the possibility of quality if required. It is important to aim for chopped well-shaped bales to produce fewer bales/ha. This will reduce both baling and wrapping costs.”

“Chopping a silage bale has an effect on silage intake with sheep but not cattle. Wrap within three hours at the storage site if possible. Use six layers of wrap rather than the normal four if silage is 30 per cent DM, a coarse crop or baled during high day time temperatures.”

“In periods of broken weather silage quality is continually falling. D value can decline by as much as nine per cent per week in a severely lodged crop.”

“In such cases try to mow when the grass is dry. Auto swath to reduce damage to the ground while also reducing contamination. When compromise is required, compromise on dry matter because the quality is king.”

“When making silage, it is important to plan ahead to ensure quality feeding for next winter. Farmers need to consider the stock they keep, their feed requirements and how much silage they need.”

“A one cap fits all approach to silage making will increase costs or reduce performance if a number of different stock types are present on-farm. It is important to maintain soil fertility and to harvest grass at the correct time to ensure quality.”

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