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.