21 November 1997


Aerobic spoilage can reduce

the nutrient value of silage

by a third and reduce

intakes. ADAS nutritionist

Philip Haigh details when

spoilage is most likely to

occur and how best to

prevent it

AEROBIC spoilage in silage occurs when a sealed silo is opened and air enters. Under these conditions some micro-organisms, which have been dormant in the absence of oxygen, suddenly multiply, resulting in deterioration of the silage.

In the clamp this deterioration is shown by a rise in temperature and pH, the appearance of moulds, and a reduction in the residual sugar and lactic acid content.

Aerobic deterioration of silage is undesirable. It is associated with high nutrient losses of up to 30% of the total dry matter. It is also likely to reduce voluntary intake and impair health, and may even cause livestock death because of the production of toxins or organisms such as listeria.

It is particularly likely to occur in silages which are used for buffer feeding in summer. And its appearance is more common in warm, wet winters than dry, cold ones.

Aerobic spoilage

Wet, poorly fermented butyric silages rarely suffer from aerobic spoilage, whereas maize and high dry matter grass silages are prone to it. The wet, poorly fermented silages are heavily consolidated, which prevents the entry of air into a silo. Such silages also contain butyric acid and high levels of ammonia – factors which help to prevent aerobic spoilage.

Conversely silages which have a high starch or residual sugar content, such as maize silage or high dry matter grass silages respectively, are susceptible to aerobic spoilage, particularly when they are inadequately consolidated and made in silos which have a large area of exposed face.

Silage making techniques, additives, clamp face and feeding management will help prevent aerobic spoilage.

Prolonged wilting, slow filling of the silo, together with inadequate consolidation and a delay in sealing a silo once it is filled, all contribute to make aerobic spoilage more likely. This is because they help to increase the aerobic micro-organisms which cause aerobic spoilage.

As for additive use, the UK Forage Additive Approval Scheme has a category C2 – aerobic stability – which lists those which are effective in preventing aerobic spoilage. To achieve this the additive must have, in five separate experiments when compared with untreated silage, significantly reduced the incidence of aerobic spoilage. The best method of doing this is to measure the reduction in carbon dioxide produced over a set period of time. However, the fact that the additive significantly reduced the temperature or pH may also be used.

Chemical salts

Several types of additive are approved – including chemical salts. Some of these products only have approval in this category, whereas others are also approved in category C4 – to reduce ensiling losses. In these chemical products the main active ingredients include sulphites – effective preservatives widely used in the human food industry. They are available in either liquid or less commonly granular form and applied at 2 litres/t or 0.25-0.5 kg/t. Other additives, for instance those containing formic acid and some inoculants, have also gained approval.

Frequent removal of silage from a clamp will limit deterioration at the silo face. Use of a block-cutter, which does not disturb the layers of silage remaining in the silo, rather than the use of a fore-end loader which disturbs the silo face is desirable to reduce the risk of aerobic spoilage.

The most obvious and perhaps most effective way of preventing aerobic spoilage is to ensure that stock eat the silage faster than the bugs attack it. This may be done by ensuring that the rate of progress through a silo is at least 10cm (3.9in) a day. To achieve this silos should be as long and narrow as possible in order to minimise the surface area of silage which is exposed to the air.

Despite the best management techniques, when silage is removed from the clamp to be fed by itself or as part of a mixed ration, air is introduced. This can lead to aerobic spoilage and major nutrient losses in the feed trough, particularly in warm weather.

To minimise this problem, little and often feeding strategies may be adopted. However, it is essential to avoid restricting intakes by limiting feeding availability. It may also be beneficial to avoid using feed components which can accelerate aerobic spoilage, for instance materials high in sugar such as molasses.

Silage additives which specifically prevent aerobic spoilage, either added at ensilage or at feed-out will also assist in minimising the risk.n



&#8226 Good consolidation and fast filling of silage clamp.

&#8226 Additives with approval in the C2 category will help.

&#8226 Frequent removal of material and use of block cutter at silage face.

&#8226 Little and often feeding strategies, particularly in warm weather.

Judging last years maize silage competition…risks of aerobic spoilage have been minimised on this wide clamp face by using a block cutter.

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