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.

  • What DM should I aim for?

    Aim for at least 28%, but only if you can achieve this within 24 hours, preferably 12 hours. DMs above this may well lead to higher DM intakes but not necessarily to higher animal production; field DM losses will also be higher and the risk of aerobic spoilage will be significantly increased.

    It is worth finishing the clamp off with a few loads of direct cut grass as this will help seal the surface and reduce aerobic spoilage.

    How can I tell what DM the grass is?

    Take a few representative grab samples of the swath and squeeze them.


  • What happens when silage ferments well?

    Obtaining a fast, efficient fermentation is critical to the success of the ensiling process. In silage fermentations dominated by homofermentative lactic acid bacteria, crop sugars are rapidly converted, mainly to lactic acid. This is the strongest acid produced during a silage fermentation so produces the fastest pH fall, from about pH 6 in the fresh forage to around pH 3.8-4.5 (depending on the crop and DM) in the final silage, as well as the lowest fermentation losses. In less efficient fermentations some of the lactic acid is replaced by the weaker acetic acid and/or neutral ethanol which results in a slower pH fall.

    A rapid pH fall reduces protein breakdown and reduces the activities of undesirable bacteria, minimising the production of highly undesirable products such as butyric acid and ammonia which would reduce silage palatability. The lactic acid bacteria in inoculant additives aimed at helping with the initial fermentation are homofermentative.

    A high proportion of lactic acid in the total acids and a low level of ammonia are both indicators of good fermentation.

  • Why should I consider making bales?

    Originally bales tended to be one way of avoiding having to invest capital in a new clampThey were also useful if you wanted to make a bit more silage and the clamp was full.  Now, improvements in baling and wrapping equipment means that baled silage can be every bit as good as clamped silage and, because of potentially lower losses, may cost less too.  This makes bales a first option for many farms rather than something to fall back on. Having some bales of 1st cut means you don’t have to open the clamp for autumn calvers.  Over 25% of grass silage is now baled.

    Substituting big bale silage for hay also has advantages as it simplifies and improves sward management.  You can use the same seed mixture and fertiliser regime for all of your conservation area.  You will also increase the total dry matter that can be produced per hectare as you will be using more productive, earlier heading varieties.

  • Should I pull the sheet down over the face at night?

    No, this is a very bad idea as it will create a warm, humid area behind the sheet, encouraging yeast and mould growth.  Always keep the sheet rolled back off the face but weigh the front edge down to prevent air getting under the sheet. During periods of very heavy rain it can be pulled down temporarily to prevent rain soaking into the face.

  • How quickly do I need to move the face back?

    Move the face back at least 1 metre per week in cold weather and 2 metres per week in warm weather, especially with silages over 30% DM.

  • Haylage


    Haylage is part-way between hay and silage. The grass is cut slightly earlier than for hay, between heading and flowering. It is wilted and baled at 50% to 65% DM, instead of being left to dry to 80% DM as with hay.

    It is then fermented like silage, but a more limited fermentation takes place because it is made using drier material. Haylage is popular with horse owners as it does not contain the high levels of dust and mould often found in hay.

    Method of Preservation

    Good lactic acid fermentation is still necessary, so the same management practices apply as for silage. Choose an additive that will ensure a fast, efficient fermentation and inhibit the yeasts and moulds that cause heating and moulding.

    Due to the high dry matter, secondary clostridial  fermentation should not be an issue. However, it can occur in wetter pockets or if an animal carcass is present, leading to animal health problems. Botulism in horses is one example.

    Spoiled or poorly fermented haylage will also increase the risk of Listeria, which can affect all livestock, but is particularly serious for sheep. A pH of less than 5.6 will kill Listeria. Good quality, well-fermented haylage should be pH 4.5 - 5.5.

    Nutritional value

    Because of its higher moisture content, haylage should be fed at around 1.5 times the fresh weight you would normally feed hay. Good haylage will have a pleasant acidic odour, be uniform in colour and feel moist.

    Good quality haylage will contain around 10-13% crude protein and have a dry matter digestibility of 65-70%.  Less leaf loss occurs during harvesting than for hay because the material is moister, resulting in higher protein content. Haylage is also more palatable and digestible than hay, so there is very little wastage at feed-out.

    Advantages of haylage

    • Highly palatable
    • Produces less dust than hay
    • Fewer problems with moulds
    • Less weather dependent than hay
    • Entirely mechanised production
    • Lower field losses than for hay
    • Higher nutritional value than hay

    Disadvantages of haylage

    • Low in nutritive value, particularly protein
    • Limited intake potential
    • Very weather dependent / field losses can be high
    • Can be dusty and high in mould spores, increasing the risk of lung infections in livestock and handlers
    • Needs to be stored in dry conditions
  • Silage feeding tips

    If self-feeding, the clamp should be low, access should be controlled to keep the face tidy and straight and take the top off regularly to prevent collapsing and air pockets forming.

    If trough feeding, do not put out more than you require and do not allow uneaten silage to build up in the bottom.

    If TMR feeding and the silage is high DM and/or the weather is very hot, twice daily feeding may be necessary to reduce waste.

  • Why should I use a silage additive?

    It is very important that silage ferments rapidly as this preserves more true protein and minimises the activities of undesirable microorganisms. A natural silage fermentation is brought about by lactic acid bacteria (LAB) on the crop. However, they are often present in relatively low numbers and are not usually the best type of LAB for bringing about a rapid and efficient fermentation so fermentation will be slow, require more sugars and lead to higher losses. Silage inoculants apply high numbers of specially selected LAB that will dominate the natural LAB and bring about a faster, most efficient fermentation. Some inoculants have also been proven to bring about animal performance benefits.

    Silage additives (inoculants and chemical preservatives) that inhibit the yeasts and moulds that cause aerobic spoilage are also available.

    Silage additives can offer a number of benefits but you need to make sure you use the right one for the job and ask to see independent evidence to show it has been proven to work, otherwise you could waste your money.

    Potential benefits from additives:

    Improve Fermentation
    •    Faster
    •    More efficient

    Reduce DM Losses
    •    Fermentation
    •    Effluent
    •    Aerobic spoilage

    Improve Animal Performance
    •    Increased DM intake
    •    Increased digestibility

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

  • Are Listeria a problem with bales?

    The bacterium Listeria monocytogenes is found in soil and slurry as well as small numbers on grass. It infects sheep and cattle causing listeriosis which leads to abortions and encephalitis.  Sheep are more susceptible to infection because differences in their teeth make it easier for the bacteria to access the nerves.  Listeriosis has increased significantly in sheep since the introduction of big bale silage. With cattle, infection of the eye by Listeria causes “silage eye” a painful ulceration which is treatable.  This happens because the animal tends to push its head into the more palatable centre of the bale and this may allow infected grass stalks to poke it in the eye.  It is obviously less of a problem with chopped bales.

    Listeria can survive in low numbers in silage but will not multiply so long as air is excluded and the pH value remains below about pH 5.  In the presence of air, however, they can survive at much lower pH values.  If a lot of air gets in moulds will grow causing the pH value to increase and providing ideal conditions once again for Listeria to grow and multiply.

    Listeria are more likely to survive and grow in big bale silage than clamp silage.  This is the result of a number of factors.  The low density and high DM content associated with baled silage results in a slower, less extensive fermentation.  In addition, bales have a very high surface area to volume ratio, exposing more of the silage to air if the bag or wrap becomes damaged.  Listeria growth is usually associated with the outer layers of bales where they can be present in very high numbers, especially if the silage is visibly mouldy.

  • How does the feed value of bales compare with clamped silage?

    There is no reason why baled silage should be inferior to clamp silage if grass of equal quality is ensiled.

  • What factors will help achieve a good fermentation?
    • Use a high quality sward and frequent cutting at an early stage of growth.
    • High dry matter content – less sugars are required to achieve a stable fermentation.
    • Adequate sugar in the crop – enough to achieve a stable fermentation.
    • Appropriate chop length – drier material requires a shorter crop for good compaction.
    • Rapid clamp filling – ideally clamps should be sheeted every night and, if filling is going to take longer than 2 days, it is essential.
    • Correct compaction – the drier the material the more important the rolling and sealing to exclude air.
    • Application of a proven inoculant – this applies high numbers of specially selected bacteria to drive the fermentation
  • Does feeding grass silage cause acidosis?

    The optimum pH value for the rumen is pH 6.2.  If conditions become too acid the fibre-digesting bacteria and protozoa are killed.  This results in reduced intake and digestibility, hence the cow takes in less nutrients leading to poor body condition and fertility and other health disorders, eg laminitis.

    In order to prevent the rumen pH value from altering significantly the cow produces copious amounts of saliva (150 litre/day).  If the cow did not produce saliva, eating silage could (in theory) reduce the pH value to below pH 3.

    It is not just the pH value of the silage that is important, however, but also the buffering capacity (Bc).  In fact, the latter is more important as it is the Bc which indicates how difficult it will be for the rumen to maintain its optimal pH value, not the pH value of the silage.  The Bc of a silage is a measure of how much saliva the cow will need to produce to maintain the rumen at pH 6.2 if it eats that silage.  Buffering capacity is only partly dependent on pH value as a lot of other compounds contribute to the total Bc, eg proteins.  It is possible to have two silages with the same pH value but with quite different Bc values.

    If two silages have identical pH values the silage with the higher proportion of lactic acid (higher LA:VFA ratio) will usually have a lower Bc and it will be easier for the rumen to maintain the optimum pH value.

    Many of the acidosis problems blamed on feeding low pH value silages are in fact the result of feeding the wrong supplements alongside the silage, eg a readily fermentable carbohydrate that will cause rapid acid production in the rumen so making matters worse.