Why Analyse Silage?
Matching the dietary nutrient supply with that of the animal’s requirements is crucial in maintaining production and reducing losses. Failure to do this will result in over and/or under supply of nutrients which in turn reduces production efficiency and profitability. Analysing silage is a crucial factor in this process and as silage is the most variable component of the diet frequent analysis is justifiable. This is as true for baled silage as it is for clamped silage as both can contribute significantly to the overall forage nutrition within your complete ration.
How to Analyse your Silage
It is important when analysing any feedstuff to obtain a representative sample. Within this context bales offer particular challenges, but also particular advantages.
Clamp Silage Sampling
Clamps are relatively easy to analyse as you can take a cored sample in a diagonal line across the top of the silage clamp. Be sure to core as far into the silage clamp as possible, and to take at least 4 cores from each clamp.
Bale Silage Sampling
So how many bales should you sample?
The best approach is to sample as many as possible. However, whilst it is not possible to
sample every bale, it is advisable to take samples from bales made at different times over the season, and from areas of the farm that you know produce different quality forage. This approach will enable bales with different compositions to be identified and thus fed to the stock where they will best meet their dietary requirements.
How do you obtain a representative sample from a bale?
One problem with bales is the variation in dry matter from the top to the bottom of the bale. As the dry matter content increases this becomes less of an issue, but silages less than 25% DM will have a significant DM graduation through the bale. Therefore it is important to sample all the way through the bale. Two approaches are possible. One is to core the bale from the top to the bottom ideally in three places across the bale and mix the samples well before sending for analysis. The second approach is during feed-out if, and only if, the bale is being processed through a chopper this will enable a well mixed sample can be obtained.
Once all samples from a given clamp or set of bales have been taken mix them well and pack into a plastic bag, remove all the air from the bag before sealing and send immediately to the laboratory. It is advisable to send samples for analyses during the first part of the week to avoid the risk of them ‘sitting around’ not being analysed over the weekend, when there nutrient content could be changing.
The Analysis
The silage analysis can be split predominantly into two parts firstly those parameters associated with the initial forage such as Metabolizable Energy, Crude Protein, Ash, Neutral Detergent Fibre and Acid Detergent Fibre, will be similar irrespective of ensiling methodology and reflect by and large the quality of the forage at harvest. Secondly there are those that are associated with fermentation such as, pH, Lactic acid, Total Volatile Fatty Acids (sometimes split into Acetic, Propionic and Butyric Acids) and Ammonia-N. These parameters will indicate how well the preservation process has been controlled. Finally there are two parameters that reflect both crop quality at harvest and fermentation, these are Dry Matter and Water Soluble Carbohydrate (WSC) or sugars. If there has been an in efficient fermentation process then some of the dry matter in the original herbage will be converted to water and carbon-dioxide. Thus the dry matter content of the silage will be less than that of the ensiled forage. The WSC concentration is not only a reflection of the level of WSC in the ensiled forage but also a gauge of the efficiency of fermentation, with a higher level being associated with a more efficient fermentation.
There are also some differences in fermentation between bales and clamps. In general the fermentation in a bale is more restricted than clamp resulting in baled silages having a higher pH and WSC concentration but a lower level of total and lactic acids.
