Silage Advice

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

  • What time of day is best to cut?

    Surface water will evaporate faster from the standing crop but cut as soon as possible after the crop has dried. Although sugars tend to be a bit higher in the afternoon the difference is not usually very great and should not delay the decision to cut.

  • Will using L. buchneri cause a reduction in DM intake?

    Silages treated with L. buchneri will have a high acetate content and for many years it has been said that high acetate levels in silage will lead to reduced intakes, however, the evidence for this is extremely controversial with evidence both for and against. It seems likely that the explanation for this is that in the past high acetate silages resulted from a poor initial fermentation which would also have resulted in a number of other end products that are not measured in a typical silage analysis. It may be that it is these, rather than acetate itself, that are causing reduced intakes, perhaps due to palatability issues - human beings are not put off by high levels of acetate – we put it on our chips as vinegar.

    High acetate silages resulting from treatment with L. buchneri are very different as, in this case, the acetate results from secondary fermentation of lactate, the only other product being 1,2-propanediol. There is no evidence from published trials to indicate that high acetate silages resulting from buchneri secondary fermentation cause intake problems, even at acetate levels above 5% DM. In fact, there seems to be little evidence for buchneri treatment having any effect on animal performance - positively or negatively.

  • 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 moulding), especially at feedout. Generally crops that are difficult to ferment are aerobically stable and vice versa.

    Crop Main Issue
    Low DM grass Fermentation
    Legumes Fermentation
    High DM grass Aerobic spoilage
    Maize 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 homofermentative 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 moulds also produce mycotoxins which can adversely affect animal performance, health and fertility.

  • Do I need an additive for maize?

    When ensiled at the recommended DM of 32 to 35% there is still enough sugar present for fermentation to achieve a stable low pH. Maize has a low buffering capacity so the pH falls fast, often to a pH as low as 3.5. Natural fermentations tend to result 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 maize 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 minimise aerobic spoilage and clamp management at ensiling and feedout are crucial, the aim being to limit air exposure as much as possible. An additive designed to deal with this issue will also help – suitable inoculants and chemical preservatives are available.

  • How is silage quality judged?

    The quality of silage can be judged in a number of different ways, all of which are vitally important for maximum animal performance.

    Nutritional value – characterised by measurements like ME, crude protein, ‘D’ value factors that are influenced mainly by the quality of the initial crop

    Fermentation quality – characterised by measurements like pH value, ammonia-N, lactic acid content, volatile fatty acid content. Good silages are characterised by a low pH value, low ammonia-N (less than 10% total N) and a high ratio of lactic acid to volatile fatty acids (LA:VFA).

    Keeping quality – this refers both to the stability of the initial fermentation, ie whether it is at risk of undergoing a clostridial secondary fermentation during storage, and to the susceptibility of the silage to aerobic spoilage on exposure to air.  If the final pH is low enough for the DM of the silage there should be little change in the fermentation parameters during storage.  Unfortunately, the better the outcome of the fermentation, the more at risk the silage is to aerobic spoilage as lactic acid will not inhibit the yeasts and moulds that cause it.

  • Do I need an additive for maize?

    When ensiled at the recommended DM of 32 to 35% there is still enough sugar present for fermentation to achieve a stable low pH. Maize 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 maize 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 minimise aerobic spoilage good clamp 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.

  • Should I wilt?

    Wilting has a number of advantages and should be attempted, but only if conditions permit.

    • It raises the dry matter of the material which means that less water needs to be transported from field to clamp, speeding up that stage of the harvesting process and reducing the size of clamp required.
    • Effluent is reduced, almost completely above 30% DM, especially important now that regulations have been tightened.
    • Wilting reduces the amount of fermentation required to produce a stable silage so less sugars are required.
    • It reduces overall protein breakdown.
    • It reduces the chances of a poor fermentation as some of the microorganisms responsible for bad silage will not survive in higher dry matter silages.
    • Wilting increases intakes but production will not necessarily increase by as much.

    There are also some potential negatives associated with wilting:

    • Higher DM silages are more susceptible to aerobic spoilage
    • Making it requires more labour and equipment

    If it looks like wet weather is on the way it is better not to try to wilt but to ensile rapidly whilst conditions are dry.  Otherwise you risk having to leave the grass lying in the field for an unknown period, deteriorating all the time.  If you delay cutting to wait for a better spell of weather the ‘D value may have fallen significantly by the time you have another opportunity.

  • Why can’t I have both quantity and quality?

    In a normal year the optimum date for cutting is usually a compromise between quantity and quality, because as the crop bulks up the quality reduces.

    As a grass tiller develops the fibre content increases and the degree of lignification increases leading to a reduction in digestibility. The ‘D’ value falls about 0.5% per day after heading.  Protein concentration also falls, further reducing feed value.

    typical changes in nutritive value of grass

  • 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 (eg acetic acid), non-acids (eg ethanol) 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 undesirably 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.

  • Should I have the grass analysed before I cut?

    This is essential if you believe there may be a problem, eg high nitrates. It will also give you information regarding the ensilability of the crop and this will help you decide just when to cut. You must get the results back within 24 hours for them to be useful as the grass composition can change very rapidly.

  • What height should I cut at?

    It is advisable to set the mower to leave at least 7-8 cm (3 inches) of stubble. Although cutting lower would increase the yield, the extra material is of poor nutritive value and there is a greater risk of soil contamination. Cutting too low also delays regrowth as it removes the tiller and leaf buds and may even kill some plants. If swaths are to be ‘rowed up’ a longer stubble will help to avoid soil contamination problems without reducing dry matter yields for the season as soil moisture will be better conserved and regrowth will be faster.

  • How far ahead of the forage harvester should I mow?

    Not too far. If the grass is wilting rapidly there is a danger of the dry matter getting too high.  Similarly, you do not want to risk having to leave a large acreage down if rain stops harvest.

    Remember that the crop probably dries very little overnight but is still at risk from unpredictable weather.