Silage Advice

We have put together many of the frequently asked questions, but please contact us if there's something we haven't covered.

You can also access a range of expert advice and practical tips through our new intiative Cut to Clamp.

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Cut to Clamp aims to raise the profile of good silage as a vital part of modern farming, showing how it can really make a difference to overall farm efficiency and profitability. Our step by step guide covers all 6 key stages of silage production; Cutting, Wilting, Harvesting, TreatingClamping and Feeding.

  • Do I need an additive for high DM grass silage?

    With high DM grass the fermentation is slower and the silage will stabilise at a higher pH. The slow fermentation allows more time for undesirable microorganisms to be active as well as increasing the breakdown of true protein.  Inoculation speeds up the process as well as making it more efficient with lower DM losses.

    High DM silages are also at higher risk of aerobic spoilage at feedout with potentially high losses and the risk of mycotoxins so good management is essential but additives are also available to help reduce aerobic spoilage.

    Remember – an additive is not a substitute for good management.

  • Can I feed silage to horses?

    More and more grass silage is being fed to horses instead of hay. Although well fermented low DM silage can be fed to horses, it is usually baled at a dry matter of 50% or higher when is referred to as “haylage”.  If made properly it is considerably more nutritious and more palatable than hay and there should be none of the health problems associated with dusty hay.  Square bales are usually preferred to large round bales as they are easier to feed in wedges.  More recently it has become possible to make small round bales of around 35-50 kg fresh weight.

    More mature grass is usually used for haylage; a ‘D’ value of 60-65 is adequate.  It is more important that the feed should be consistent.  Do not chop the grass short for horses, they prefer it fairly long.

  • Why it is important to wilt for bales

    Wilting is essential when making bales for the following reasons:

    • Better fermentation
    • Lighter weight bales
    • Less bales per hectare to cart and store
    • Prevent effluent leakage
    • Makes solid, better shaped bales that wrap and stack better
    • Bales retain their shape better – deformed bales can let air in
  • How can I avoid high nitrate levels at harvest?

    The best way is to get your application rate right in the first place. However, prolonged periods of dry weather cannot be anticipated and can ruin even the best made plans.  Remember that, after a prolonged dry spell, rain will cause rapid nitrogen uptake by the plants.

    If high nitrates are suspected make sure you have a representative sample of the grass analysed. If the nitrate level is above 1,000 ppm (0.1%) you should not ensile. Wait a few days and analyse again.

  • What level of losses can I expect when making and feeding silage?

    The total losses arise from a number of sources, the relative importance of which depends on the crop DM. For instance, with wet crops effluent is important but with higher DM crops aerobic spoilage losses can be very high.

    The largest potential losses are from aerobic spoilage, mainly at feedout. Provided a good fermentation has taken place fermentation losses are small. If you do everything properly you can still expect total losses of 10-15% but if you do not pay attention to detail you could easily have losses of over 30%. Silage that has undergone significant aerobic deterioration can result in total losses above 50% but as much of these losses are invisible carbon dioxide this is often not realised on farm.

    Range (%)
    Field 2-10
    Fermentation 10-15
    Effluent 0-5
    Aerobic spoilage 10-30
    Total 20-50

    Well managed system

    Well Managed SystemIn Germany, Honig was able to relate dry matter losses to temperature increase for crops of different dry matters. He found that with a 30% DM crop there was a 0.23% loss in DM for every 1°C increase in temperature above ambient.

    Based on this, for a 30% DM silage the following losses can be calculated:

    DM Loss (%)
    Increase in temperature (°C) Days heating
    3d 5d 7d
    5 3 5 7
    10 6 10 14
    15 9 15 21


  • Legume silage


    Legume is the common term for a plant species that has an association with bacteria known as Rhizobia. Legumes include: white and red clover, Lucerne, Sainfoin, Bird’s-foot trefoil or lotus, Lupins, Forage peas and beans.

    Rhizobia live on the root nodules of the legume and fix atmospheric nitrogen, making it available to the plant. This means there is little need for nitrogen fertiliser. Consequently, legumes are important crops for organic farmers.

    The popularity of legumes has waned over the years as they are difficult crops to grow. However, in recent years, more tolerant, disease resistant varieties have been developed and interest in these crops is increasing again.

    Method of Preservation

    The principle of ensiling legumes is the same as for grass silage, but legumes have a low sugar and high protein content, resulting in a high buffering capacity. This means that legumes are difficult to ferment, which can result in poor quality silage. Consequently, they need to be treated slightly differently.

    Rapid wilting (48hrs), assisted by the use of a mower-conditioner with rubber rollers, to at least 30% dry matter helps to make the crop easier to ferment using additives. IGER (2001) recommend that the dry matter must be over 45% if no additives are used. Legume silage can be clamped or baled in the same way as grass and maize.

    Advantages of  Legume Silage

    • Environmental benefits due to the fixation of atmospheric nitrogen
    • Reduction in the need for artificial fertilisers
    • High protein
    • High production per hectare
    • Reduction in concentrate feed costs

    Disadvantages of Legume Silage

    • Narrow harvest window
    • High input costs
    • Difficult to ensile
    • Make increase nitrogen excretion
  • What is the best way to remove silage from the clamp?

    It is vitally important to prevent air penetrating the face to any depth. A block cutter is the best option as it causes minimum disturbance and leaves a neat, tight face. A shear grab is also effective but there is more face disturbance which leads to loose silage falling down. This should be picked up and fed immediately. Failing this, a silage grab is adequate provided you move the grab downwards when removing silage, rather than lifting it upwards. The worse possible option would be a bucket on a fore-end loader lifting the face, leaving a loose, cracked face and a lot of fallen silage.

    DM losses at feedout vary tremendously, eg over a 4 day period they could be as little as 1% with a well compacted, well-sealed silo with an undisturbed face or as high as 15% where compaction and sealing have been poor and the face has been loosened.

    Is a block cutter or shear grab worth buying?

    These are probably the most cost-effective pieces of machinery you could invest in. They are the best way to keep the clamp face tight and tidy – provided the blades are kept sharp.

  • Wholecrop silage


    The popularity of ensiling wholecrop cereals has increased in recent years as they offer a good alternative or complement to traditional fermented forages.

    Wholecrop provides a good source of starch and is generally cheaper to produce than grass silage, but it is low in protein. Cereals are a high yielding crop that can be grown in areas which are unsuitable for maize. They offer great flexibility. As harvest takes place after first cut silage, a decision can be made on how much wholecrop is required. Any remaining area can be left to produce mature grain for sale or crimping.

    Method of Preservation

    Similar to grass silage, the crop is fermented in a clamp to produce lactic acid, which preserves the crop and makes the grains more digestible.

    Wheat is most commonly used due to its high yields. Other good grain to straw ratio and digestible grains are used and any cereal crop can be ensiled.

    The cereals are harvested at a range of dry matters.

    As the crop is relatively high in dry matter, it is difficult to maintain a good fermentation. To reduce heating, an additive which combines an inoculant with an aerobic spoilage inhibitor is recommended.

    Fermented Wholecrop (35-45% DM)

    The ideal range for fermenting wholecrop is 35-45% DM. 40% is best, when the grain is at the soft cheddar stage.

    High DM Wholecrop (56 - 65%DM)

    Due to high grain maturity, wholecrop of this dry matter should be harvested using a primary processing mill. This is to ensure maximum digestion when the forage is fed. Due to the high DM, fermentation will be limited, but there is a high risk of aerobic spoilage, causing heating and nutrient loss.

    Advantages of Wholecrop

    • Complement to grass and maize silage
    • Good starch and fibre levels
    • Flexible crop
    • Increases Dry Matter Intake (DMI)
    • Early harvesting

    Disadvantages of Wholecrop

    • Low protein
    • Narrow harvest window
    • Wasteful fermentation and high DM losses
    • Animal performance does not always reflect increased DMI
  • How important is it to get rid of air?

    Although growing crops may have >109 (1,000,000,000) bacteria per gram on them, most of these will be aerobic (require oxygen) and will die out as soon as conditions in the silo become anaerobic (no oxygen present). This is important as their activities do not contribute to the fermentation process; indeed their activities would waste sugars required for fermentation.  Lactic acid bacteria are the main bacteria involved in a silage fermentation and are able to grow in the presence or absence of air but the way they break down sugars differs. To maximise lactic acid production air needs to be absent.

    Fungi (yeasts and moulds) are a particular problem for silage as they are responsible for aerobic spoilage (heating and moulding), especially at feedout. Aerobic DM losses at feedout can be extremely high. Moulds need air to grow and in its absence produce spores that can germinate and grow when it is present again. Yeasts grow much faster in the presence of air but will survive in its absence. It is the ones that that can utilise lactic acid in the presence of air (lactate assimilating yeasts) that cause the biggest problem.

    By filling the silage clamp quickly and rolling well, the amount of air trapped initially is minimised and quickly used up. As well as allowing the proper fermentation to begin sooner, it minimises yeast numbers at opening which reduces the risk of aerobic spoilage.

  • What is the best way to weight the sheet down?

    It is best to apply an even pressure over the whole surface of the clamp to prevent the sheet flapping and air getting in. Touching tyres can be used on unroofed clamps and either tyres or hay/straw bales on roofed clamps.  A few tyres or bales scattered over the top is not sufficient.

    Alternatively, use a heavy duty woven tarpaulin with gravel bags around the edges and seams. Although more expensive to buy they can be reused many times.

    Note: 10 cm of surface waste actually arises from a much deeper layer of previously good silage. DM losses in the surface waste can be as high as 65%.

  • How short should I chop?

    Chopping makes it easier to compact the grass in the clamp, especially important for higher DM crops, and releases sugars for fermentation. However, don’t overdo it; the move to higher DM grass as well as more maize and wholecrop cereals in the diet has led to concerns about low butterfats due to there being insufficient effective fibre in the diet. Short-cropped grass is also easier to transport as more can be carried per load, but remember to take appropriate precautions to prevent physical losses from the trailer.  

    Normally the long fibre in rations is provided by grass silage and chop length should match the circumstances.

    DM Issues Chop Length (cm)
    >30% compaction 1.5-2.5
    20-30% effective fibre 2.5-5
    <20% slippage,effluent 5-7.5


  • Who invented silage?

    The word silo comes from the Greek word 'siros' which means a hole or pit in the ground for storing corn. It is known that the Greeks and Egyptians were familiar with ensiling as a technique for storing fodder as far back as 1000 to 1500 BC. In parts of Northern Europe grass was being ensiled in the early 18th century but it was not until the latter part of the 19th century that it became more widespread.

    The first book on silage was published by a French farmer, based on his experiences with green maize. He advised rapid filling of the silo and stressed the importance of keeping it air-tight during storage. A year later an English translation was published in the USA and American farmers quickly adopted the new technique.  Although the French and American farmers were very enthusiastic it was not until 1882 that a talk given at the Reading Show of the Royal Agricultural Society stimulated interest in Britain.  By 1886 there were apparently 1,605 silos in the country, with farmers here concentrating on ensiling grass rather than maize.

    Unfortunately silage making in the UK suffered a set-back in 1885 when a book was published recommending that silage should best be made by heating it initially to at least 50°C by aerating it. Although the silage produced was palatable it was of very poor nutritional value and losses were very high. Nevertheless the method persisted until the middle of this century.