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.

  • How can additives influence silage quality?

    In general an additive will not increase the nutritional value of a silage above that of the original crop but can increase it relative to an untreated silage, eg due to reduced losses of more digestible nutrients. Some enzyme-based additives claim to increase the nutritional value above that of the original crop due to direct fibre digestion.

    Fermentation quality can be significantly affected by the use of a silage inoculants. Those aimed at improving fermentation make it faster and more efficient fermentation, resulting in more palatable silages and lower losses. Good silages would have a low pH, low ammonia-N (less than 10% total N) and a high ratio of lactic acid to VFA (LA:VFA). An exception to this is silages treated with an additive containing Lactobacillus buchneri as such silages will have a higher pH and lower LA:VFA ratio due to them undergoing a secondary fermentation of lactic acid to acetic acid, a weaker acid.

    Inoculants that help achieve a faster fermentation to a lower final pH will minimise the risk of a clostridial secondary fermentation so there will be little change in the fermentation parameters during storage. Some inoculants, eg L. buchneri, also influence aerobic stability by producing antifungal compounds such as acetic acid. Antifungal chemical preservatives, such as sorbate, propionate and benzoate can also be applied.

  • Do I need an additive with bales?

    With baled silage, fermentation is slower and restricted due to the longer chop length and the higher DM of the grass. There can also be a lot of variability between individual bales, especially if the grass sward varies across the field; in a clamp such variability gets evened out to a large extent.

    Bales are also more susceptible to aerobic spoilage due to their high DM and large surface area to volume ratio – 27% of the volume of a 4 foot bale is in the outer 5 cm. They are also less dense compared to clamped silage, although improvements in balers have meant densities have been much increased over the years.

    Another issue with bales is their susceptibility to growth of Listeria bacteria due to their higher pH and increased risk of aerobic spoilage. Listeria only need a small amount of air infiltration, eg from pierced wrap, to be able to grow.

    They can benefit greatly from application of an additive that will make the fermentation faster and more efficient as well as reduce the risk of aerobic spoilage.  

  • When do I need to stop grazing the silage fields?

    Over-wintering cattle can induce poaching and soil contamination on medium to heavy soils, producing a rough surface and increasing the likelihood of soil contamination when mowing.  Grazing by sheep is beneficial, however, as it removes stemmy and dead grass leading to more digestible silage.

    Ideally you should remove stock before any spring growth appears.  Failure to remove them by the end of January will reduce 1st cut yields and also increase the risk of contamination with manure.  If you do intend to spring graze you should get the stock off by the end of March.

  • How important is pH fall rate and final pH?

    The faster the pH value falls the sooner the wasteful activities of the live plant material and undesirable microorganisms will stop.  This will reduce losses and result in a more palatable silage.  It will also conserve more sugars for conversion to lactic acid so that less sugars will be required to achieve a successful fermentation. If the pH is slow to fall and/or sugars run out before a stable pH is reached, undesirable microorganisms such as clostridia can take over as they can convert lactic acid to butyric acid, a much weaker acid, so the pH increases (clostridial secondary fermentation).

    The lower the crop DM, the lower the final pH will need to be to stabilise the fermentation

    Effect of pH on grass silage fermentation quality

    the effect of the type of fermentation on the rate of pH fall

  • Will using Lactobacillus buchneri cause a reduction in DM intake?

    For many years it has been said that high acetate levels in silage lead to reduced intakes, however, the evidence for this is extremely controversial with evidence pointing both ways. It may be that it is other fermentation end products that we don’t measure but are also being produced in a poor, high acetic silage that could be the issue rather than acetate itself. (Human beings are not put off by high levels of acetate – we put it on our chips as vinegar). A number of researchers have suggested that acetate levels above 5% DM could be an issue but such levels are not seen very often, even in a buchneri treated silage. On the whole there seems to be little evidence for buchneri treated silages affecting animal performance, positively or negatively.

  • How much slurry can I apply?

    Typically 6% DM dairy cow slurry contains 2.6 kgN, 1.2 kgP and 3.2 kgK per m3 so it is a very valuable mineral source. The P is 50% available and the K 90% available but N varies with the time of year and type of soil. Consult tables in order to calculate how much your slurry will supply. It is also important to apply within the permitted time periods and not to apply too much in order to avoid run off and potential environmental contamination.

  • What if it rains?

    Leaving it lying will increase losses and potentially make it more difficult to ensile due to loss of sugars and an increase in spoilage microorganisms. So, provided it is not pouring, you should bring in what is already mown as quickly as possible. If the delay is more than 6 hours, sheet and seal the silo. If you have a lot of grass down and experience heavy and continuous rain you may find yourself in a salvage situation.

  • Why silage and not hay?

    Hay used to be the traditional method of forage conservation in the UK but has been superseded by silage in recent years.  In 1970 about 80% of the grass conserved was as hay but this had fallen to less than 30% by 1990 due to a 5-fold increase in silage to about 46-50Mte.

    Good hay is more palatable than silage due to the high sugar content and the reduced protein breakdown.  The breakdown of hay in the rumen also results in a more synchronised release of energy and protein.  Its main disadvantage is its reliance on having 5 or 6 days of good weather, something which cannot normally be guaranteed in the UK.

    In order to aid the drying process it is preferable to have a stemmy, low yield crop, the latter usually achieved by application of low levels of fertiliser.  The crop at harvest is therefore already of relatively low nutritive value.  Further losses in feed value will be incurred during field drying, especially in poor weather, and this can result in a very variable product.

    Silage is made from more digestible material and is not so reliant on the weather.  Techniques for making silage have improved greatly over the last few years, making it possible now to produce high quality silage routinely.  All in all, silage making makes more efficient use of the grass, reducing the need for bought-in feeds and increasing profitability.

  • 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.

  • How important is clamp 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.  Clamp management is one of the most important aspects of the silage making process.

    • Line the silo walls – allow a 2m overlap with top sheet
    • Fill fast in thin layers – max 15cm (6 inches)
    • Compact well
    • Do not overfill
    • Seal quickly
    • Weight top sheet well
    • Sheet overnight or if bad weather stops harvest
  • How should I prepare the clamp?
    • Clean out any old silage and, if necessary, pressure wash.
    • Ensure effluent channels are not blocked
    • Repair the walls and base, sealing any cracks properly – remember, heavy clamp machinery running close to silo walls exerts enormous pressure on the walls.
    • Remove nails, old sealing materials and any other uneven obstructions from the walls.
    • Cover any rough areas of the wall with bags to prevent damage to the main sheeting.
    • If the silo walls are constructed of sleepers, porous concrete or earth they should be lined completely with polythene.
  • How important is it to fill the clamp quickly?

    Rapid filling and sealing of the clamp is one of the most important aspects of silage management.  The longer the clamp remains open the more sugars will be wasted by respiration so they will no longer be available for fermentation.  It will also allow yeasts and moulds longer to multiply which will make the silage more likely to spoil later on opening.

    Initial aerobic phase dry matter losses can be less than 1% if the clamp is filled and sealed quickly but can increase to over 7.5% in a clamp left open for 3 days.

    Using a contractor will enable you to fill the clamp faster but it is important it is not filled so fast that rolling can’t keep up.