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Taking the right silage samples can help save on feed costs - a video guide

Taking time to collect a silage sample which properly reflects the clamp could be the most profitable half-hour spent on-farm. Louise Hartley reports.


What is the most profitable half hour you spend on the farm? Adam Clay, ruminant manager at Trouw Nutrition GB suggests it could be taking regular, accurate and representative silage samples.

Silage sampling
With conserved forage commonly making up 50 per cent of dairy cows’ diet, knowing the nutritional value of silage and how it changes as you move through the season is vital.
Mr Clay says: “There is potential for error at every stage of feeding cows, from rationing, mixing and feeding out, but one area often overlooked is sampling.
“Fertilising, harvesting and clamping the grass is okay, but this hard work is pointless if the silage is not fed correctly and accurately balanced with the relevant concentrates. 
“Key to this is making sure the sample is representative of the silage you are feeding cows.
“Taking one sample from a section of the clamp is no good. During feeding you will move across the clamp face, taking silage from top to bottom – the sample must represent this.”



Taking the sample

Taking the sample
In order to achieve a representative sample of the entire clamp face, several sub-samples should be taken and mixed together.
Take nine individual samples in a ‘W’ shape across the whole clamp face.  
Taking the sample
For each sub-sample, dig out silage to about 15cm (6in) deep in the clamp face – a screwdriver is useful for this. This will remove any weather-affected silage or secondary fermentation from oxygen exposure, which could distort results.

Taking the sample

Mix the nine samples evenly on a clean surface or in a bucket. Discard half, mix again and continue this process until you have about 500g or a minimum of half a sample bag’s worth of silage. 
Taking the sample
Having enough silage in the sample bag is important to allow laboratory technicians to analyse it properly.
Mr Clay advises against taking core samples from further within the clamp as they are not representative of the silage being fed to cows.
Taking samples through the sheet straight after harvest and before the clamp has been opened is also not good practice.
Mr Clay says: “Taking core samples or samples through the sheet is like finding a needle in a haystack. Collect samples from the silage face to get the most representative and useful results.
“Wait a minimum of three to four weeks – ideally six weeks – after clamping before collecting the sample to ensure the pit is anaerobically stable and is no longer undergoing microbial fermentation.”
Taking the sample
When sealing the sample bag, make sure all the air is squeezed out to stop further fermentation before the sample is tested.
“When ready, send the sample to the lab as soon possible, ideally the same day via first class post and avoid sending it on a Friday or weekend. 
“If you do need to wait another day before posting, do not freeze the sample, but keep it in the fridge,” adds Mr Clay.
Many feed suppliers offer silage sampling free of charge, but the standard cost of a near infrared (NIR) analysis of a grass silage sample is £12.50 per sample. Results are often emailed direct to farmers within a day of the silage sample being received.
“For a 200-cow herd, it is only six pence per cow to ensure you are meeting the cow’s requirements,” he says.

Laboratory analysis

Laboratory analysis
Once the sample is received at the lab, results from the analysis are usually emailed out within 24 hours.
Trouw’s headquarters in Ashbourne tests about 52,000 samples of forage per year.
Some 99 per cent of samples received by the lab, which range from grass, maize, hay and different crops, are tested via NIR analysis.
In peak season, the lab tests between 350-400 forage samples per day.
Mr Clay says: “Samples arrive at the lab by post at about 8am. Each sample is logged and analysed by trained technicians in a ventilated and air-conditioned room to avoid distorting the results.”

Variation over time

Variation over time
Silage quality changes as the season progresses, not necessarily due to fermentation, but because most clamps contain multiple cuts taken from multiple fields of different leys and grass types. 
The proportion of first, second and third cut also changes as you move through the clamp as it is buckraked in a ramp shape.
The graph is based on data from the study’s 10 farms and shows what happens if the diet is not continuously rationed against changing forage quality in winter.
“Based on initial analysis, a diet was formulated to produce 30 litres per cow per day with a daily dry matter intake of 12kg of silage.  We then resampled the clamp monthly and calculated what the diet was now worth, based on the same 12kgDM from silage and the same level of supplementation.
“As the season progressed the silage quality changed, meaning cows were producing less from forage and as the rest of the diet was not changed to reflect this, total yield dropped.  If the clamp had been fed through the winter based on the initial analysis."
If the ration had stayed the same during the 160 day winter, the potential milk loss would have been £169 per cow.
Mr Clay says: “The main reason for the drop in production would be due to a fall in silage DM as they moved through the clamp, which meant cows were being underfed. 

Variation across the clamp face

Variation in DM and ME across the clamp face can be substantial and costly if the ration is based on a sample from only one section of the clamp.
Surprisingly, the biggest variation in a clamp face is from top to bottom.
Mr Clay says: “Many would expect the bottom of the clamp to be wetter and lower in energy than the top because of effluent draining, but due to compaction and increased aerobic fermentation the bottom is often higher in DM and ME.”
If the sample on which the ration is based is not representative of the forage being fed – typically, the whole clamp face – there could be major feeding errors, he says.
The study took silage samples from 10 farms every month from October to March and looked at DM and ME variation within the clamp face.
On average, DM at the bottom of the clamp was 1.5 per cent higher than at the top (at 34.25 per cent compared to 32.75 per cent), equivalent to 2.4kg milk per cow per day.
The difference in milk yield potential between the middle and sides of the clamp was as much as 0.85 litres per cow per day.
Based on silage analysis from the middle of the clamp at 33.75 per cent DM, cows would need to be fed 35.5kg silage to achieve a DM intake 
of 12kg per day.
If the sample was taken from the top, at 32.75 per cent DM, each cow would require 36.65kg silage fresh weight, an extra 1.15kg, to achieve the same DM intakes.
“Analysis allows you to know the silage DM and recalculate how much freshweight you are feeding to deliver the required DM intake – it is easy to trim the amount of silage back or add more.
“Overestimating silage intake means cows will not eat the silage being fed and therefore will not receive the right amount of concentrates either.”
The ME also varies across the clamp face. The bottom of the clamp had an average ME of 11.1 while the top was 10.6. This is equivalent to one litre of milk.

Top tips for silage sampling

  • Wait about four weeks after clamping before taking the sample
  • Sample at least monthly
  • Take nine samples across clamp face in a ‘W’ shape and mix them thoroughly 
  • Dig into the clamp about 15cm (6in) to get the sample
  • Squeeze air out of bag to stop an aerobic fermentation
  • Post straight away or refrigerate
  • Do not send a sample on a Friday or on a weekend
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