Silage Advisory Centre

How to Analyse your Baled Silage

It is important when analysing any feedstuff to obtain a representative sample.  Within this context bales offer particular challenges, but also particular advantages. 

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 wise 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.

The Analysis

Silage produced in a bale has a different fermentation process to that in a clamp and so some parameters may not be what you would expect.  Table 1 shows the results of experiments conducted at the Institute of Grassland and Environmental Research (IGER, now IBERS) in Aberystwyth with direct comparisons between 3 forages, hybrid ryegrass, red clover and lucerne, harvested at the same time and ensiled either in a bale or a clamp. Parameters associated with the initial forage such as, Dry Matter, Metabolizable Energy, Ash, Crude Protein, Neutral Detergent Fibre and Acid Detergent Fibre, will be similar irrespective of ensiling methodology.   However, those associated with the fermentation can be different, this is predominantly due to the fact that even in the most highly chopped baled silage the forage is still far less processed and of a longer chop than that in a clamp.  So less water soluble carbohydrate (WSC) is released from the forage to fuel the fermentation.  This ultimately results in general, but not always, to lower concentrations of fermentation end products.  As a result the pH is often higher in silage produced in bales than clamps at the same dry matter.  In turn lactic acid concentrations are lower.  However, due to this slower fermentation the undesirable end products such as acetate and ammonia-N can on occasions be higher in bales than clamps, but attention to good silage making practice will eliminate these issues and can ironically result in these end-products being lower than that found in clamp silage. 

Finally because less sugar has been used to fuel the fermentation the concentration of WSC is higher in bales than clamp and this is excellent news for your stock as it improves the utilization of the silage protein in the rumen!

Table 1 – IGER experiments comparing composition of forages ensiled either in bales or clamps

Dr Dave Davies is an independent scientist for the Silage Advisory Centre (www.silageadvice.com), dave@silagesolutions.co.uk