The value of dividing walls

Ask any operator and they all know what a good clamp looks like, nice and big with plenty of room to turn round in. And they have a point, it can speed up the filling process, reduce likelihood of damage and makes life much simpler, but those clamps with dividing walls have something to offer that makes it worth all the bother – a return on the investment.

What do dividing walls offer me?

Splitting a clamp into different bunkers is obviously a benefit when it comes to storing and accessing different crops or cuts. Not all silages are equal and you might well want to get at the first cut silage before the 3rd cut. Having access to different silage crops also enables you to blend a ration to suit the recipients – be they four legged or housed inside a concrete tank, but as we all know, nothing comes for free and those walls are not cheap. So how do the costs stack up in terms of payback for clamp division walls? Budgeting the costs is quite straightforward but quantifying the benefits is a bit more complex. The most important benefit – I would argue – is the reduction in spoilage and losses on the silage face.

We have previously explored the optimal width of silage clamp design and those rules are what govern the economics of division walls. It’s all about keeping the face fresh and working back through the silage fast enough. As a rule of thumb the target should be about 2m per week. Face losses can quickly be as much as 30% of the total silage dry matter so it’s really really important to get this right. What is even more important to remember is that these losses are invisible – you won’t see black or rotten silage, you will never see the feed value disappearing. The only way to demonstrate these losses is though silage analysis at the point of feeding. 

Calculating the savings?

So to the maths, we will assume a hypothetical dairy farm feeding grass silage as follows:

-       400 cows feeding 10 tonnes of forage per cow over 6 months

-       Grass accounting for 75% of the silage ration so 3000 tonnes

-       All the grass stored in a single clamp 28m wide x 28m x 3m high

A square footprint is probably the cheapest layout to build a clamp for any given tonnage of storage capacity. The problem with this layout is that the silage face is too wide. If the cows are housed for 180 days, then progress through the clamp will only be around 155mm per day or just over 1m per week. This will result in significant face losses of silage DM. At these rates or use, even if you are getting everything else right, dry matter, chop length, compaction, sealing etc, losses at the face can be expected to be around 20%.  

What are the losses costing?

The cost of making and ensiling a tonne of silage will vary depending on scale and set up, but it’s likely to be around £25-£30 per tonne. So in this case you are looking at losses of £15,000 to £18,000 in face losses – every year……

By introducing a dividing wall to the clamp the feed face rate can increase to 2m per week. This will reduce losses massively, by around three quarters so down to about 7.5%. This is still costing you £3,750 to £4,500 but it’s a potential saving of £11,250 to £13,500.

What will a dividing wall cost?

There are lots of ways to construct a dividing wall from movable freestanding units to fully permanent cast-in walls but the total costs will be in the region of £1000 per meter once the walls are installed and fitted with safety rails and sealed. So for this example we are looking at about £28,000 for the wall. The potential savings mean that this an investment with a payback of between two and two and a half years!

We must not ignore the possible costs due to slower daily feed out routine. Working in the clamps in the example would not be a problem, but in some cases you might add a few minutes to each diet feeder load – so what is that going to cost?

Let’s assume it adds half an hour a day, at £40 per hour this comes to £3,600 extra cost. Even so the payback period is extended to 2.8 years to 3.6 years

Introducing a dividing wall into your silage clamp might just be one of the better investment paybacks any farm can make.

What about year round silage feeding?

It doesn’t really matter if you are feeding silage to a dairy herd housed 365 or to an AD plant, these loss figures are just as important. Whilst the clamp volumes are bigger, the rules remain the same – or worse. Worse because feeding silage from a clamp in the warm summer months leads to even greater face losses. The microbes that are chewing through your dry matter have a much bigger appetite on a warm June afternoon than they do on a cold February night. So its even more important to move through the silage by at least 2m per week – ideally 2.5m in the summer months. 

Introducing dividing walls and getting the face width right might be the single most important thing you can do to reduce in clamp losses. By building a narrow clamp you might not get thanked by the silage contractor or the guys feeding out every day but you will be thanked by whatever is eating the silage – and the bank account.

If you want to discuss the pros and cons of dividing walls in your silage clamps or any of the other aspects of silage making covered in this series – contact Jeremy Nash at Jeremy@silageconsultant.co.uk

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