How to predict silage clamp losses

No one likes losses – unless they are on the bathroom scales, but of all the silage losses those in-clamp aerobic ones are the most expensive. As we have seen elsewhere there are things you can do to try and control these. Here we are trying to predict what these losses might be and where they might be occurring. 

We need a caveat before getting too excited on this subject; prediction is not an exact science. What we are trying to do here is provide some tools that can be used to help your decision making processes. In the meanwhile this might explain some of the thinking behind the “rule of thumb” mathematics you might have read elsewhere.

Why focus in on the Aerobic exposed face losses?

The focus must be on the losses that occur as soon as the face is exposed to the air and the oxygen it contains. This is for two main seasons, firstly these are the biggest losses you are going to experience (probably) and secondly because they are invisible.

Invisible losses are never going to end up in the muck pile or left in the feed trough, they disappear into thin air. That’s because your silage is (hopefully) a great feed source for not only your livestock or AD tank, but it is also the ideal feedstock for bacteria, fungi and yeasts. The fermentation process that has protected and preserved the crop for the months since the forager went home to the shed did not kill all these hungry microbes. These guys have been in a state of dormancy whilst the pH has been low and oxygen has been unavailable. As soon as the conditions change and oxygen is once again available then the microbes come back to life and get to work on the silage.

As these unwanted squatters eat up your silage energy and protein they turn the feedstock into gases that disappear into the atmosphere and heat that rises as steam. The silage might still look the same but much of the feed value has gone. There are things you can do to limit this as we have seen elsewhere, but feed-face progression is maybe the most useful.

Why 2m per week feed face progression?

The figure of 2m per week or 300mm per day has been around for many many years and there doesn’t seem to be much evidence to suggest it’s not suitable. This figure was based on temperature measurements and silage analysis from the exposed face. Over the years a number of things have changed that can improve aerobic stability of the silage such as increased dry matter, reduced chop lengths and improved consolidation / compaction.

So is there an argument that 300mm is too conservative as we now have all these other improvements? I would argue that on the contrary, there is some suggestion that we might need to increase the 300mm figure. And the reason for this madness? Climate change. It’s undisputed that winters are on the whole warmer than they were 40 years ago. Warmer temperatures lead to more microbial activity so what we have gained with one hand we have lost with the other.

With a base line of 2m per week (300mm per day) we can expect around 10% loses of feed value from aerobic microbial activity. Now by using some maths we can predict that the losses might be for different feed-face progression.

Hungry Flemming Shear Grab

In order to do this we need to look at the farm equipment used on the clamp. I take the size of the shear grab and its “usual” bite and work out how long the silage is exposed until the grab comes back and takes another bite on the same bit of face. At 300mm per day that time comes out at around 56 hours of exposure.

With a less optimal feed-out, the progression might be 200mm per day and then the face exposure jumps to 84 hours. This is 1.5 times the base exposure so should we expect 1.5 times the losses or 15%? Err maybe not….

Why losses are not proportional to exposure

The trouble with simple maths is the world isn’t that simple. The microbes that have been sitting dormant not only start feeding when the clamp is open, they start reproducing as well. And this leads to a pretty much exponential growth in the losses. Obviously these processes are governed by time and temperature as well as food and oxygen availability so the outcomes are not easy to predict. But however we look at it, the longer it’s exposed, the more silage you are going to lose. And that includes the time it spends in the feed trough or intake system to the AD tank – but that’s another story.

Albutt Shear Grab at the silage face

On a practical front, pick a spot on your clamp – bottom left hand corner or wherever - and see how long it is before the grab gats back to the same spot. If it’s less than a two and a half days then that’s OK. If it’s 3 days or more then you need to think about what changes you could make to speed up face progression. Maybe adding a division wall would be sensible, as we looked at before, in some instances this can pay for itself in very little time.

Increasing the exposure time of the clamp face by 1.5 times, with a cost of silage at £30 per tonne will be costing you £1.50 per tonne in losses as a very low estimate. Take the predicted losses from 15% to just 20% and is £3.00 per tonne. And remember that loss applies to all the tonnes stored in the clamp – every year!

You are very quickly looking at tens of thousands of pounds for a small clamp and hundreds of thousands for bigger bunkers.

If you want any further information or help predicting the losses in your silage clamp, or to discuss any of the other aspects covered in this series – contact Jeremy Nash at jeremy@silageconsultant.co.uk

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