This is a question I am regularly asked and one I periodically ask myself. There is absolutely no doubt that additives are expensive, somewhere close to £1 million per tonne, but the manufacturers and suppliers make some very bold claims for enhanced performance by using silage additives. There is also a steady stream of users that will testify to the benefits of using additives. So why do I have nagging doubts that question the value of using additives?

Some of these doubts are probably due to the invisibility of the actions of additives. The driver of the chopper can see and feel the benefits of sharpening the knives or adjusting the shear bar of the machine. But the actions of a silage additive won’t be seen until the clamp is opened and the silage reaches its final destination. To further compound the problem, it’s almost impossible to do an “on farm” trial. With crop protection spray or fertilizers, it’s easy to miss a bout or half a field and to readily see (or not) the difference the “black magic” is making. But with silage, the whole clamp tends to ferment as an entirety so even though you might treat only half the silage with an additive in a trial, if you store it all in the same clamp – the trial will be just about worthless. You don’t really get an accurate trial over different cuts or seasons either as there are just too many variables to single out the additives actions.

So you might well end up thinking “should I just use the additive and hope for the best?”

That might be some people’s solution but I think it’s possible to dig down into the science to help make an informed value judgment. So what’s in the additive and what is it trying to do? I’m going to avoid the history of additives (because this isn’t a book) and concentrate on what the options are in the early 2020’s. Most additives are an inoculation of bacteria and, in some cases, preservatives in the form of salts. The majority of the additives used in Western Europe include Lactobacillus as the primary bacteria inoculation in some form or other. As you are probably aware, Lactobacillus bacteria digest free sugars – usually glucose – to produce lactic acid that is, very helpfully, the ideal acid to preserve forage in the absence of oxygen. So that makes sense, we want lactic acid in the clamp to preserve the silage and these bacteria produce it. In most cases the inoculant will be Lactobacillus Plantarum and that’s important because the second part of its name tells us where it usually comes from – from plants.

 Lactobacillus Plantarum is not a rare or obscure bacteria, it’s common to almost all agricultural crops and (in almost all cases) will be all over your forage crops prior to harvest. This begs the obvious question

Do I need additives to make good silage?

And the answer to that is definitely no – you don’t, you can make great silage without an additive. So why are additives used and what can they do for you?

By using an inoculant you are ensuring the “good guy” bacteria – the Lactobacillus Plantarum (LP) are dominant. This is important because there is a battle going on as soon as the crop hits the clamp. There are loads of different micro organisms all competing to thrive inside the clamped silage. In good silage, the LP will become dominant (eventually) and this produces the conditions for stable silage storage as this bacterial strain ONLY produce lactic acid. By adding a whole load of LP at the beginning, we make sure they reach dominance more quickly and that’s a good thing – isn’t it? Maybe, and maybe not, let’s look at the two sides of the argument.

Firstly the rapid blooming of LP produces loads of Lactic acid, rapid drop in pH and stable silage. In trials the pH of treated silage drops rapidly in the first 24-36 hours compared to untreated silage. After 48hrs there is not much difference in pH and at 7 days the treated and untreated samples are the same. So the inoculated silage is stable sooner - about 24hrs before the untreated silage – that doesn’t sound much of an improvement does it matter? Well it’s not much but it does matter because the crop is respiring, degrading and losing nutrient value from the moment it’s cut until stable silage conditions are achieved. So a 24hrs improvement is significant.

Along with LP, Chlostridia bacteria (CB) are also present on the crop and these will breakdown valuable sugars and proteins to produce butyric acids. LP produce acids without using up proteins and will create conditions where CB can’t thrive. So getting LP dominant earlier does help get stable silage more quickly, protecting the proteins and reduces losses further.

On the other hand, we need to consider the negatives. Firstly the LP need certain conditions to thrive; they need a clean environment – so they don’t have to compete too hard to flourish, they need a good feed supply (the sugars in the silage) and a lack of oxygen. If the conditions aren’t good, neither the LP present on in the crop, nor those in the additive will thrive. So you have to get the basic conditions right before you can ever see any benefit from using additives.

Finally there can be potential disadvantages of this very rapid lactic acid production. Losses can occur at any time in the silage life cycle. One of these potential sources of losses occurs when the clamp is open and the silage is vulnerable to aerobic instability. Aerobic instability is caused by micro organisms that survive the low pH of fermentation and then become active once exposed to oxygen. They use up protein and energy form the silage and also can produce moulds and toxins that make the silage unpalatable. This obviously doesn’t really come to light until the clamp is opened and is more likely to occur in higher dry matter silages, and clamps with longer chop lengths. In trials it has been shown that the presence of aerobic stability is not influenced by the overall silage acidity (pH) or populations of moulds and yeasts. The only thing that can influence aerobic instability is the level of acetic acid so you need to ensure there are good levels of acetic acid in high dry matter silage. Up until now we have been stressing how important it is to get good lactic acid levels – and fast. So where does acetic acid come in?

Acetic acids have different properties to lactic acids and this seems to the key to solving the aerobic instability issues. Acetic acids are produced naturally by Lactobacillus Buchneri (LB) bacteria, amongst others, and these can thrive in the clamp during the early stages of fermentation. However, once the LP are dominant they produce so much lactic acid the conditions are too much for the LB and their activity stops. Now here is a potential problem; an extremely rapid drop in pH by inoculated LP silage doesn’t give the LB time to produce much acetic acid. This means the inoculated silage reduces early losses but can make the silage vulnerable to aerobic instability losses once the clamp is opened.

To combat this, additive manufactures add either LB inoculant or Potassium Sorbate to their base additives. Potassium Sorbate is a preservative salt that acts as Sorbic acid, an acid that is very very similar to acetic acid. As it’s action is unaffected by lactic acid levels, this ensures aerobic instability is restricted.

So what can we draw from all this?

·      Additives can’t compensate for poor practice and conditions so make sure you get all the details correct before you consider using an additive or it’s just a waste of money.

·      Choose the additive carefully and understand what it is going to do in the clamp.

·      In high dry matter or longer chop lengths, only use an appropriate additive over a simple Lactobacillus Plantarum inoculant.

·      Evaluate the costs very carefully, at £1.20 to £1.50 per tonne treated, you need to be making a 5% reduction in losses of feed value just to cover the additive costs.

 If you want to discuss the cost versus benefits of silage additives with an independent consultant or to discuss any of the other aspects of silage making covered in this series – contact Jeremy Nash @ jeremynash1@btinternet.com