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Silage Analysis

We are at that time of year when thoughts are turning to housing cattle and their requirements over the winter period.

There is no doubt that having access to quality stored silage is crucial for many farmers -  whether it is grass, wholecrop, maize or a combination of these - as this will form the main component of the winter diet.  As such, it is important to perform accurate silage analysis so that farmers can correctly estimate the amount of concentrate required, thereby ensuring consistent animal performance and in turn maximising profit margins.

Sampling should be carried out no earlier than six weeks after crops have been ensiled. Three to four cores to a depth of 1.5 metres should be taken diagonally from clamp silage (with holes taped to stop air ingression), or at least five bales from each batch of baled silage. If the sub samples prove too large they should be thoroughly mixed, reduced and sent off to the laboratory early in the week so samples do not remain in the Post Office over a weekend.

Silage analysis will allow you or your advisor to predict animal intakes of Dry Matter, energy and protein, and help formulate a diet which will maximise animal performance. Some of the nutritional elements of your silage analysis will include Dry Matter (DM) - the amount of material left after all water is removed. This should be in the range of 25-35% as very wet (or indeed very dry) silage can reduce intakes. Wet silages tend to be extensively fermented, high in acids and low in rumen structure - all factors which reduce intakes.  Rations should not be based on silage weight but on DM as this will give quite different results. For example, 45kg of silage at 20% DM equals 9kg DM, whilst 45kg of silage at 30% DM equals 13.5kg DM.

D-Value, the digestibility of the DM, is closely related to the crops’ maturity at cutting date, particularly in grass silage. There is some evidence to suggest that in wholecrop cereals the D-Value will not change as much as in grass. Normal D-Values for grass silage are in the region of 64-72 with very high quality silages at higher levels.

Metabolisable Energy (ME) is a measure of the energy content (MJ ME/KG DM) available to the animal after losses in faeces, urine and methane. It is calculated from the D-value and high values range from 11.1-12.8.

pH is measure of the acidity of the clamp with the normal range being between 3.8 and 4.2. Low values indicate acidic silage which may result in reduced rumen function and acidosis. In cases like this a rumen buffer is required, or a product such as Biotal’s SC AcidEase, in order to address the problem. In general, wetter silages will have lower pH figures and dryer silages will be higher.

Crude protein is a measure of the total nitrogen content of the silage x 6.25 and may include any residual fertiliser nitrogen left in the sample. Normal levels for grass silage are between 11-15 %, and around 9% for wholecrop. This is not necessarily an accurate measure of available dietary protein. Low levels will, however, require additional supplementation, and those with higher levels may contain more rapidly degradable proteins, which will not be as useful to the rumen microbes.

There are many other elements within your analyses that will help give an indication of silage quality. Sampling will help you decide the best approach for feeding your cattle or sheep in order to maximise animal performance. Start planning now so that you can make full use of your silage this winter.


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