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.

  • Is it really necessary to sheet the clamp overnight?

    You should always sheet down at night or if filling stops for any longer than 6 hours. It doesn’t take long and  will minimise air exposure and prevent rain ingress with uncovered silos. 

    After sheeting, the oxygen level throughout the silo starts to fall quickly due to the continued activities of plant enzymes and aerobic microorganisms so it should all be gone in less than 30 minutes. If you do not sheet it will remain high in the outer layers. This will delay the onset of fermentation and allow aerobic activity to continue, especially near the surface, increasing losses - you may see a layer of poor quality silage when you open the clamp.  Prolonged aeration will lead to an increase in the numbers of yeasts, increasing the risk of aerobic spoilage at feedout losses.

    Note: You can get an idea of how much  aerobic activity is occurring by pushing your hand into the forage the next morning – you will feel the heat.

  • Golden rules for making bales
    • Wilt to at least 30% in 24h
    • Rake up to form box swaths of uniform width and density
    • Make dense, well-shaped bales
    • Net to the edge (or over) so no soft air traps
    • Wrap within 2 hours
    • Use a good quality wrap
    • Consider using a lighter colour of wrap
    • Use enough layers of wrap
    • Don’t leave them in the field
    • Handle gently and as little as possible after wrapping
  • Advantages and disadvantages of bales


    • Low capital investment
    • Flexible harvest and feedout
    • Quality as good as bunker
    • Low DM losses (<5-10%)
    • Low storage costs
    • Low pollution risk
    • Can be used in TMRs
    • Can sell surplus


    • More expensive to make
    • Unsuitable for low DM
    • More variability
    • Prone to damage
    • Labour/time at feedout
    • Plastic displosal
  • Do I need to manage grass swards for bales any differently?

    No, manage them to produce top quality forage, not second rate.  You should always use good quality grass for bales as courser grass will not consolidate so well, trapping more air and hence being more likely to suffer from moulding.

  • Should you use an additive on haylage for horses?

    A proven bale-specific additive can bring many benefits:

    • A faster, more efficient fermentation for more stable haylage with lower losses and improved palatability
    • More consistent fermentation so reduced bale variability
    • Reduced risk of moulding during storage
    • Delayed moulding of a newly opened bale, extending the safe feeding period
  • How do inoculants differ?

    Inoculants contain different species of bacteria as well as different strains of the same species. Bacterial species differ in the same way humans (species Homo sapiens) differ from cows (species Bos taurus). But Holsteins, Jerseys and Herfords, although all the same species, are very different in their characteristics. Think of them as being equivalent to different strains of a particular bacterial species. For instance, there are many different strains of the species L. plantarum, eg MTD/1, and they all have very different characteristics

    Inoculants designed to improve the initial fermentation nearly all contain Lactobacillus plantarum as this species has been shown to be particularly good at bringing about a rapid silage fermentation. But most strains of L. plantarum don’t start working until the pH has fallen to below 5.5 so to get the fermentation started other ‘helper’ species, eg Streptococcus faecium or Pediococcus, need to be included. Sometimes more than one strain of a particular species is also added as these may have different characteristics.

  • How effective are chemical preservatives at reducing aerobic spoilage?

    A number of different chemical preservatives are available, the most common being potassium sorbate, sodium propionate and sodium benzoate with potassium sorbate being the most widely used preservative in the food and feed industry worldwide.

    Mode of action

    In contact with water, the chemical forms an equilibrium between the undissociated and dissociated acid molecules. It is the undissociated acid that inhibits the yeasts and moulds that cause aerobic spoilage as it can cross the cell membrane. In the cell it dissociates again, causing the pH to decrease which disrupts various cell enzyme processes.

    The relative amounts of the undissociated and dissociated acid depends on the pH of the solution and the dissociation constant (pKa) for the acid. The three preservatives above are required to work in the pH range of silage, ie around 6 down to less than 4 and as the pH falls the amount of undissociated (active) acid increases so the antifungal activity increases. This makes them particularly suited for use in silage.

    Of the three preservatives above, sorbate has the potential to be more effective in silage as it can work over the whole pH range encountered during the ensiling process. This has a practical advantage as it can inhibit yeasts earlier during ensiling, helping to prevent them increasing in the early stages.

    Preservative Yeasts Moulds Working pH range
    Sorbate +++ +++ 3.0-6.5
    Grass - +++ 2.5-5.5
    Maize/Lucerne +++ +++ 2.5-4.0

    -No effect on microbial growth
    +Inhibits growth, the more + the bigger the effect

  • What factors will prevent a good fermentation?
    • Introducing soil into silage – this is a particular problem below 25% DM when the clostridia bacteria from soil contamination can flourish and turn a potentially good silage into a very poor one with high DM losses (clostridial secondary fermentation).
    • Late or heavy fertiliser application – assume 2.0 units N per acre (2.5 kgN/ha) utilised per day of growth and apply no more than can be taken up before the planned cutting date.
    • Late slurry application – do not apply less than 10 weeks before cutting if surface spreading. If injecting, applications up to two weeks prior to cutting should be fine.
    • Application of dirty water or silage effluent – do not apply to silage ground.
    • High grass nitrate-N levels, ie above 1000 ppm (0.1%).
    • Bad sealing – if the sheet or wrap is damaged or of poor quality, air can get in.
    • Over-rolling wet young grass – with high quality direct cut or minimal wilted material under 20% DM, condition lightly, chop longer and roll sufficiently to level and tidy only.

    Usually it is a combination of several of these factors, rather than any one, that lead to a poor fermentation.

  • Maize silage


    Maize is now the most popular cereal crop conserved as silage. Though essentially a tropical plant, breeders have developed earlier maturing varieties, enabling northern areas to grow maize successfully.

    Method of preservation

    The method of preservation for maize silage is basically the same as for grass.  

    Maize should be ensiled at 32 to 35% DM. The high DM and sugar contents, along with a low buffering capacity, make it easy to ferment, although a good inoculant can reduce fermentation losses and some can bring additional animal performance benefits.

    The biggest issue with maize is its susceptibility to aerobic spoilage, so it’s worth applying an additive that can deal with this. This may contain chemical preservatives, specific bacteria or plant extracts, all designed to inhibit yeasts and moulds during ensiling and feed-out.

    Advantages of Maize Silage

    • High DM and energy
    • Easily fermented
    • Potential to increase DM intake, milk yield and milk protein in dairy cows
    • One harvest per year
    • Direct cut, no wilting
    • Compliments grass silage

    Disadvantages of Maize Silage

    •    Not suitable for wet or cold regions
    •    Low protein and fibre
    •    High DM and starch levels make it prone to aerobic spoilage
    •    Variable quality - weather dependent
    •    Can reduce milk fat if fed at high levels
    •    Low in calcium phosphorous and sodium

  • Can inoculants be used on low sugar grass?

    Very wet grass silage stabilises at a lower pH and the acid produced is diluted so you need more to achieve this. This means you also need more sugar and a minimum of 3% (fresh basis) used to be recommended. If an inoculant is applied, however, you could get away with significantly less as the sugars are used more efficiently.

  • Are all lactic acid bacteria the same?

    There are two main types of lactic acid bacteria (LAB), homofermentative and heterofermentative.

    Homofermentative LAB convert crop sugars mainly to lactic acid which is the strongest type of acid produced during a silage fermentation. Energy and dry matter losses are minimal. The most common homofermentative LAB species found in silage inoculants are Lactobacillus plantarum, Pediococcus pentosaceus, Pediococcus acidilactici and Enterococcus faecium.


    Heterofermentative LAB convert crop sugars to a mixture of end products, including acetic acid, a weaker acid than lactic, and ethanol which will not aid acidification. Carbon dioxide is also produced and represents a DM and energy loss.  The rate of acidification is significantly slower.


    The numbers of LAB on growing crops can be quite low and the majority are generally heterofermenters. Some of the homofermenters found grow well initially while the crop pH is still high but their growth rapidly becomes inhibited as the pH falls, eg Enterococci. This is why inoculation with high numbers of specially selected strains of LAB can lead to a much faster fermentation.

    Although heterofermentative LAB are not desirable for the initial fermentation, one such species, Lactobacillus buchneri is now commonly being incorporated into inoculants aimed at reducing aerobic spoilage as it has the ability to convert lactic acid to acetic acid, an antifungal compound. It is not particularly active during the initial fermentation, the conversion of lactic acid only taking place after the initial fermentation has been completed.

  • How does Lactobacillus buchneri reduce aerobic spoilage?

    This is a species of heterofermentative lactic acid bacteria. During the initial fermentation it competes with homofermentative lactic acid bacteria and converts sugars to a mixture of end products, including acetic acid, something which will reduce the rate of pH fall as well as increase fermentation dry matter losses, neither of which are desirable. But this unusual species can also convert lactic acid into acetic acid and 1,2-propanediol. This results in a silage with a significantly higher acetic acid level than normal and, as acetic acid is inhibitory to the yeasts and moulds that cause aerobic spoilage, it is less likely to heat and go mouldy at feedout. These activities will increase fermentation DM losses but the potential savings in reduced aerobic DM losses should more than make up for this.

    Although 1,2-propanediol is not an acid and has no anti-fungal properties, there are bacteria on forages that can convert it to a mixture of propionic acid and 1-propanol. Propionic acid is an even better anti-fungal agent that acetic acid.

    how does Lactobacillus reduce aerobic spoilage