Silage Advice

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

  • Why should I use a silage additive?

    It is very important that silage ferments rapidly as this preserves more true protein and minimizes 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 for 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 molds 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.

  • What kind of additive should I use?

    Different crops have different issues when it comes to making and feeding silage. The two main problems are achieving low, stable pH quickly and preventing aerobic spoilage (heating and molding), especially at feedout. Generally crops that are difficult to ferment are aerobically stable and vice versa. 


    Main Issue

    Low DM grass




    High DM grass

    Aerobic spoilage

    Corn Silage

    Aerobic spoilage

    Wholecrop cereals

    Aerobic spoilage


    Both issues can be dealt with using either inoculants or chemical additives.

    For fermentation you can use an inoculant containing homofermentative lactic acid bacteria to bring about a fast, efficient fermentation. Alternatively you can apply an acid product to reduce the pH directly.

    Some homomfermentative inoculants have also been shown to bring about improvements in animal performance, even in situations when the untreated silage would have undergone a good fermentation. Improvements in animal performance with chemical additives are normally only found when the untreated silage would have undergone a poor fermentation.

    For improved aerobic stability there are also inoculants available. These may contain heterofermentative lactic acid bacteria, in particular Lactobacillus buchneri which carries out a secondary fermentation, converting lactic acid into the anti-fungal acetic acid. Alternatively, there are a number of chemical food/feed preservatives available, usually based on sorbate, propionate or benzoate. Inhibition of aerobic spoilage can improve animal performance because heated silages are generally less palatable with a lower nutritional value; some molds also produce mycotoxins which can adversely affect animal performance, health and fertility.

  • Do I need an additive for corn silage?

    When ensiled at the recommended DM of 32 to 35% there is still enough sugar present for fermentation to achieve a stable low pH. Corn Silage has a low buffering capacity so the pH falls fast, often to a pH as low as 3.5. Natural fermentations tend to results in somewhat higher proportions of acetic acid and ethanol, an indication of a less efficient fermentation which could be improved upon using a homolactic inoculant, some of which can also bring about animal performance benefits. 

    However, by far the biggest problem with corn silage is its susceptibility to aerobic spoilage. Apart from potentially very high DM losses, the final silage has a lower nutritional value and may contain mycotoxins which can affect animal performance, health and fertility. To minimize aerobic spoilage good feed management at ensiling and feedout are crucial, the aim being to limit exposure to air as much as possible. An additive designed to deal with this issue will also help – suitable inoculants and chemical preservatives are available.

  • 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 Lactobacillus 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.

  • 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.

  • What happens when silage ferments poorly?

    If the initial fermentation is dominated by heterofermentative lactic acid bacteria, fermentation acidification is slower and less efficient fermentation due to the production of weaker acids, non-acids and carbon dioxide.This means that more sugar will be required to achieve the same final pH value and fermentation losses will be higher. If sugar is limiting a stable pH value may never be reached. This can allow other very undesirable bacteria, eg clostridia, to take control, changing a poor fermentation into a very bad fermentation with a much reduced nutrient value and high losses.The slower fall in pH value also means that there will be a greater breakdown of proteins, mainly due to continued plant enzyme activity.

  • What is clostridial secondary fermentation?

    This occurs before the silo is opened in the absence of air and when a stable pH value is not achieved initially, often because of insufficient sugars or contamination from soil or slurry. A particular type of undesirable bacteria (clostridia) convert the lactic acid already produced into butyric acid, a weaker acid. Some clostridia also break down amino acids, resulting in high ammonia levels and some extremely unpleasant products, eg putrescine and cadaverine. Dry matter losses will be high and the final silage is unpalatable and has a low feed value.

    Good silage                                     Bad silage

    pH4                                                  pH above 5

    Lactic acid                                      Butyric acid+carbon dioxide (=partial DM loss)

    'Protein'                                         Amines, Amonia

    The major influences on clostridial secondary fermentation

    • The dry matter/sugar contents of the crop ensiled
    • Initial forage management
    • Contamination (soil/slurry)
    • Use of an effective additive
  • What factors will help achieve a good fermentation?
    • Harvest a good stand of high quality forage and cut at frequent intervals and proper stage of growth.
    • Harvest at recommended dry matter content for the particular crop – less sugars are required to achieve a stable fermentation at higher dry matters.
    • Adequate sugar in the crop – enough to achieve a stable fermentation.
    • Appropriate chop length – drier material requires a shorter chop for good compaction.
    • Rapid filling – ideally piles/bunkers should be covered immediately after finished. For longer structures, covering should be done as you progress the wedge forward towards completion.
    • Correct compaction – the drier the material the more important the packing and sealing to exclude air.
    • Application of a proven inoculant – this applies high numbers of specially selected bacteria to drive and control the fermentation.
  • How important is packing?

    Good consolidation is probably the single most important step in silage making. It minimizes the amount of air trapped in the silo initially which will mean wasteful aerobic processes will cease sooner, allowing fermentation to begin. Yeast numbers will also be lower when the feed is opened, reducing the risk of aerobic spoilage. Packing will also bruise the forage a little, helping to release more sugars for fermentation.

    You need to be using plenty of weight; it is advised that packing tractor weight (tons) should match the forage delivery rate (tons fresh weight/hour). The rule of thumb is tractor weight/800 = tons per hour that can be adequately packed.

    With wet feeds (below 30% DM), take care not to over-pack, as excess pressure and packing will increase effluent. Do not fill the bunker too high or over-pack near the walls as wet feeds exerts a greater pressure on the walls.

    Do not excessively pack the last layer. It is more important to get the cover on quickly as most of the trapped oxygen will get used up quickly and be replaced by carbon dioxide.

    If filling over a day or more, do not pack immediately after uncovering the next morning as this will simply push out the carbon dioxide and replace it by oxygen. Only begin packing after a new layer of feed has been layered in.

  • How important is bunker/pile management?

    The quality of your silage can make the difference between profit and loss so it is well worthwhile putting in some extra effort to ensure you make it properly. Bunker/pile management is one of the most important aspects of the silage making process. 

    • Line the silo walls – allow a 6 foot overlap with top sheet
    • Fill fast in thin layers – max 6 inches
    • Compact well
    • Do not overfill
    • Seal quickly
    • Weight top sheet of plastic well
    • Cover overnight or if bad weather stops harvest or there is a delay in filling of more than 2 days.
  • 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; rather their activities 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 maximize lactic acid production air needs to be absent.

    Fungi (yeasts and molds) are a particular problem for silage as they are responsible for aerobic spoilage (heating and molding), especially at feedout. Aerobic DM losses at feedout can be extremely high. Molds 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 utilize lactic acid in the presence of air (lactate assimilating yeasts) that cause the biggest problem.

    By filling the silo/pile quickly and packing well, the amount of air trapped initially is minimized and quickly used up. As well as allowing the proper fermentation to begin sooner, it minimizes yeast numbers at opening which reduces the risk of aerobic spoilage.

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

    Move the face back at least 6 inches in cold weather and 1 foot in warmer weather.