Livestock farmers’ guide to taking and analysing silage samples

With new-season grass in the clamp, silage analysis is crucial to enable forward planning and to ensure livestock are rationed as effectively as possible with low-cost forage.

Only by understanding the exact quality of silage will it be possible to select appropriate supplementary feed and guarantee livestock are receiving what they need.

Simply guessing quality could lead to under- or overfeeding, which could compromise health and fertility or add cost. Analysis is also a vital tool to help farmers check they are hitting targets.

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How to take a silage sample

To receive useable and accurate silage analysis results, it is important to take a silage sample that is representative of what is going to be fed.

There are two main ways to sample clamped silage. A core sample uses a specialist corer to take a sample through the top of the clamp.

This can be a way to plan feeding by getting an idea of quality before the clamp is opened. However, the main method takes a sample from the face of the clamp, after it has been opened.

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Dr Stephen Whelan, research and development manager for AHDB Dairy, runs through how to take a sample from the face:

• Ideally test silage six weeks after ensiling so the fermentation process has stabilised
• Sample regularly (ideally every month) as quality can alter through the clamp due to variation between fields
• Don’t take a sample right from the face – if it has rained or been sunny it could be drier or wetter than what you are feeding
• Take 10-12 samples in a W-shape across the front of the clamp, starting half a meter down from the top. Avoid areas of deterioration, which shouldn’t be fed
• Dig about 20cm back into the face and take a handful of silage from there
• Combine all samples into a large bucket and mix well
• Pour the bucket on to clean ground, mix again, divide into four piles and take small handfuls out of each pile and pack into a clean, ziplocked, A4 bag (available from testing lab or adviser)
• Pack silage as tight as possible in bag, excluding as much air as possible. As soon as air is let in, the silage will deteriorate and won’t be representative of what is being fed
• When sampling baled silage, take core samples from five bales of the same batch and ensure any hole is sealed afterwards
• Include as much information as possible on the silage analysis sheet – date, cut number, farm details and clamp reference.

Where and how to get it tested

A farmer can send a silage sample for analysis themselves or do it via their nutritionist or feed merchant.

There are two different analysis methods: near-infrared spectrometry (NIR) or wet chemistry.

In general, a standard test will use NIR, which looks at how light is reflected back from the sample.

This uses a prediction model based on wet chemistry.

Wet chemistry specifically analyses the sample itself and as a result is more expensive.

NIR costs about £10-£15/sample or may be free if carried out through a nutritionist or merchant.

Wet chemistry cost depends on what is analysed. For a complete sample the cost could be more than £200.

Some farmers and advisers have raised concerns about variation in NIR results. But Dave Davies, director of Silage Solutions and technical secretary for the Forage Analytical Assurance Group (FAA), says if the calibration equation is correct for NIR and is carried out well, it can be just as reliable as wet chemistry.

However, with the current NIR equations, farmers analysing a novel or high-clover grass silages may be disappointed with results.

Work is currently in progress to improve clover analysis. Speak to your adviser about an appropriate testing strategy.

What do the results mean?

Once silage analysis results are received from the lab, it is important to use them as a means of assessing how successful your silage management is and how best to ration stock.

Results on a silage analysis sheet will generally be split out to cover nutritional characteristics, which are associated with the quality of the grass at point of cutting, and fermentation characteristics, which are affected by what you do from the point of cutting to feeding out.

Dr Davies runs through how to interpret results in the grass silage analysis results table (PDF)

 Top ten top tips for taking a grass silage sample for analysis

By Mike Smith, NIR service manager for Frank Wright

1. Ensure the sample is representative of what you are feeding
2. Ideally leave the clamp for six weeks before taking a sample. If you send a green, poorly fermented sample it is difficult for the lab to deal with as the sample doesn’t fit with fresh grass or silage calibrations
3. Take several samples in a W-shape across the front of the clamp and take the sample from 15-22cm into the face and mix together thoroughly
4. Make sure the sample is large enough – ideally 200-400g. Small sample are difficult to relate to the whole clamp
5. Use a clean, sealable plastic bag
6. Ensure all the air is pushed out of the bag as any air penetration will cause degradation, which means what you are sampling won’t represent what is in the clamp. Don’t use a supermarket plastic bag as there are holes in the bottom
7. Don’t leave samples in the farm office for days before sending to the lab
8. Send sample to an assured lab as quickly as possible and don’t post on a Friday
9. Write as much information as possible on the silage information sheet with the sample, including farm information and cut. Don’t put the slip in with the grass sample, as it will absorb the moisture and so affect the sample and make the writing illegible
10. Work with a nutritionist to make sure the analysis answers the questions you want