Dr Dave Davies, Silage Solutions Ltd considers how to get the most from this autumn’s silage harvests
On most farms this season silage stocks are at an all-time low, with the long winter eating into last year’s forage reserves. This has been followed by an exceptionally challenging spring and summer period, which has resulted in lower than normal harvested tonnages and many having to feed precious silage resources over the summer period. As a result, any late season harvested grass has even greater value than normal.
Undoubtedly, the biggest and most important single impact on silage quality and quantity is likely to be dry matter losses. It is often quoted that DM losses are on average between 20% and 25% in silage clamps in the UK. In 2017 I conducted a survey of silage clamps on 20 farms across the UK on behalf of AHDB, and the results of this survey give me no reason to question this assumption. These losses arise both from visibly wasted silage and invisible losses of CO2 and water during storage and feed-out.
It should, however, be possible to reduce these losses to 15% or even 10% using well known, tried and tested, ensiling methodologies. Little (or no) impact on cost of production is involved, just taking a little more time to think about the whole ensiling operation.
Putting this 25% DM loss into perspective.
One thousand tonnes of silage fresh matter harvested with a DM content of 30% equates to 300 tonnes of dry matter harvested. Losing 25% of that means you are left with 225 tonnes of DM and a financial loss of £9,000 (assuming a cost of production of £120/t of DM). Reducing these losses to 15% through thoughtful management will save you £3,600.
However, this is not the whole story. The DM losses are from the most digestible part of the silage so nutritive value is also lost. If we take a 72 D value (ME of 11.5 MJ/kg DM) grass at harvest, after 25% losses, this becomes 68 D value (ME of 10.9 MJ/kg DM) silage. Reducing those losses to 15% results in a silage with a D value of 69.6 (ME of 11.14 MJ/Kg DM). With 5 MJ required to produce a litre of milk, and feeding 10 kg DM of grass silage, this will result in an improvement of 0.5 litre of milk/cow/day comparing 15% DM losses with 25% DM losses.
Therefore, the overall gain to your business of reducing DM losses from 25% to 15% is £3,600 worth of additional silage and 15,000 litres of additional milk for every 1000 tonnes of grass fresh matter ensiled. What I have not added in is the additional concentrate costs of supplementing poorer quality silage which, to put a ball park figure on it, is likely to come in at an additional £14,000!
The big question is ‘Can you afford to allow this value to evaporate away into the atmosphere?’
Unfortunately, too many farmers either ignore, or are oblivious to, the impact these DM losses are having on both the feeding value and quantity of silage remaining in their clamps. Of all silage-making seasons this is the year to wake up and take them into consideration.
The task is, therefore, to follow precisely the best practice guidelines, which will have minimal impact on cost of production, but can significantly enhance the quantity and quality, and therefore the value, of your grass silage.
Having said all of that, this year’s late season grass silage is likely to present some additional challenges which need further thought, and these can be summarised as follows:
• The growing season and water deficit could result in lower than usual uptake and utilisation of nitrogen from manures and fertilizer. However, when the rain comes this will be taken into the plant in the form of non-protein nitrogen. This has the double-whammy effect of reducing grass sugar levels and increasing the plant’s own ability to buffer the pH decline during silage fermentation. Together these factors increase the risk of a slower speed of fermentation significantly and, as a result, secondary, clostridial (butyric) fermentation.
• The density of the sward bases could also be poorer as grass has suffered and died with the drought conditions. Open bases in the sward are likely to increase the risks of soil contamination during harvest and this will increase the risk of clostridial contamination of the harvested grass.
• Clostridial fermentations increase the % DM losses and have a major effect on reducing the protein quality of silage.
• Good sward management has been particularly challenging this season and so it is also likely that there is dead and dying material in the sward bases. This material reduces the nutritive value but also increases the risks of higher yeast and mould populations and mycotoxin risk.
• Finally, given the long hot summer with low levels of grass growth, the natural epiphytic lactic acid bacterial population is also likely to be low due to high levels of UV radiation reducing their numbers. Therefore, relying on a natural fermentation may be a risk not worth taking with such an important silage crop this season.
To combat these challenges and to give yourselves a better chance of success, and to target a reduction in % DM losses, it is essential with this late cut grass harvest season that you should think about:-
1. Cutting heights: walk the fields, inspect sward bases, and adjust the cutting height accordingly.
2. Additive: again, walk the fields, assess the amount of dead and decaying material in sward bases and consider appropriate silage additives to control both clostridial fermentation and aerobic spoilage at feed-out. The only additives that can effectively control both aspects effectively are chemical-based ones. If considering a biological additive it is even more essential than ever to choose one that applies 1,000,000 homofermentative bacteria/g of forage to ensure control of clostridia during fermentation.
3. Good clamp consolidation: as always this is the most important factor in reducing %DM losses and improving quality.
4. Good and effective sealing: including side sheets and oxygen barrier top sheets with ample top weight to ensure good consolidation and reduced oxygen ingress throughout the storage period.
My final take home message would be, this year of all years, ‘think about the value of your silage, not the cost of production!’
by Dr Dave Davies,
Silage Solutions Ltd