Guide to choosing and using silage additives

Every year farmers question whether they should use a silage additive or not. Independent expert Dave Davies of Silage Solutions gives some insight into using additives to make farmers’ decisions easier.

The most important thing to consider when using a silage additive is the economic return on investment.

Typical figures for the cost of producing silage is about £120/t of dry matter (DM) – equating to £36/t of fresh matter (FM) at 30% DM.

See also: E-learning advice on best practice silage management

A standard additive costs £1.20/t FM (or £4/t DM), which means the additive represents 3.2% of the total silage-making costs.

Silage additives are designed to do one of two things, although some additives can do both:

  • Improve fermentation in the silo to give better protein quality – not greater crude protein, no silage inoculant can do this – and increased sugar content and reduce fermentation DM losses.
  • Reduce aerobic spoilage – not secondary fermentation, this is something else – and reduce aerobic spoilage losses.

It’s important to remember dry matter losses are often invisible because there is a lot of production of CO2 and water produced, not just the visible black slime or mouldy silage on the top of your clamp or on the surface of your bales.

Savings by using a silage additive

So coming back to the example costs of production, a good silage additive, in conjunction with good silage management – for which no silage additive will compensate – should be able to reduce your DM losses during silage making such that the cost of the additive is actually less than £0.00/t. This is because you will have saved that much more silage.

The additive only needs to save 33kg DM of silage/t DM to be cost neutral. With this being the case, then all silages should use a good silage additive.

The real question should be how much silage do I need to make, because that’s where your real costs lie, not in the cost of silage additive.

See also: Silage additive pump keeps coverage even

What is a good additive?

There are many different additives on the market, claiming different things.

An additive will not replace good silage management, you will always need to:

  • Optimise nutrient quality by cutting at the correct stage of growth for the stock you intend feeding
  • Avoid soil contamination
  • Wilt correctly and rapidly
  • In clamps consolidate well and sheet up well
  • In bales bale correctly, wrap properly and store well

Having done all of this, an additive can be the icing on the cake.

Controlling the fermentation process is the most important thing an additive should be designed for. I am more reserved about additives designed to reduce aerobic spoilage because under most conditions the farmer’s own good management practices should be able to control this process.

Chemical versus inoculant

Chemicals – There are two basic types acids or buffered acids, and salts of sorbate, benzoate and nitrite. Chemicals are generally more expensive than inoculants, but can still reduce your DM losses enough to be cost neutral.

Acids are designed to inhibit the fermentation process, provided they are applied at the correct application rate.

Formic acid will inhibit the undesirable fermentation processes where as propionic acid will inhibit yeasts and moulds that cause the issues of aerobic spoilage.

Benzoate and sorbate inhibit yeasts and moulds and are often used either in conjunction with homo-fermentative inoculants or nitrite. Nitrite inhibits enterobacteria and clostridia and promotes a natural lactic acid fermentation in the silo.

Inoculants – Most inoculants contain lactic acid bacteria.

There are two different types of lactic acid bacteria.

  1. Homo-fermentative that just produce lactic acid. These can improve silage fermentation quality, reduce DM losses during fermentation and improve true protein, palatability and intake. The better fermentation results in more nutrients for the animal, but can increase the risks of aerobic stability or heating during feed-out if clamp management, which is not ideal. Homofermentative lactic acid bacteria include species such as Lactobacillus plantarum, Pediococcus, Lactococcus and Enterococcus.
  1. Hetero-fermentative lactic acid bacteria produce a mix of lactic and acetic acids and carbon-dioxide and water. They are designed to improve aerobic spoilage, but will increase fermentation losses and will result in a slower silage fermentation. The hetero-fermentative lactic acid bacteria include species such as L buchneri, L brevis and L kefira. Some inoculants contain a mix of hetero and homofermentative species, the advantages of this approach have really yet to be proven in scientific trials. Some inoculants include Bacillus species. These are akin to the hetero-fermentative lactic acid bacteria in their fermentation characteristics, but they are generally not well adapted for growth in the silo.

So the choices are: do I want an inoculant that can improve fermentation of the silage or improve aerobic stability?

I would encourage all farmers to improve fermentation as there are so many scientific trials that show improved fermentation will give better animal performance.

Improved aerobic stability can be achieved by good clamp management. Predominantly good compaction and sealing at the time of making, alongside good feed-out management.

However, if you are feeding out in the summer or your silage management is challenged beyond your control then an additive to improve aerobic stability can be cost effective.

If aerobic stability is your target the choice then is a chemical alone, a combination of chemical plus homo-fermentative inoculant, or a hetero-fermentative inoculant.

We should never compromise fermentation quality to improve aerobic stability, leading my advice to be one of the former two products types.

Finally in the UK, for green crops such as grass and clover, we need a minimum of one million bacteria/g of crop to be applied.

There is a lot of research to support this approach, so any additive not containing this number will not be cost effective and will not control the preservation as you need. Be warned: many do not.


To use an additive or not?

  1. Do I want to reduce DM losses during ensilage – Yes – use an additive
  2. Do I need to retain more nutrients in my silage – Yes – use an additive
  3. Dry matter losses aren’t important to me and neither is nutrient content – Don’t use an additive
  4. Dry matter losses aren’t important but retaining nutrients is – Use an additive

Which additive?

  1. DM less than 22% – Chemical.
  2. DM less than 28%, aerobic spoilage losses controlled by good clamp management – chemical or homofermentative inoculant.
  3. DM 28-33%. Aerobic spoilage could be an issue because of poorer management or summer feeding. Chemical or combination of homo-fermentative inoculant plus chemical.
  4. DM 28-33% Good management and winter feeding – chemical or homo-fermentative inoculant
  5. DM above 33% – aerobic spoilage will be an increasing challenge. Chemical or combination of homo-fermentative inoculant plus chemical.
  6. Baled silage – aerobic spoilage should not be an issue so chemical or homo-fermentative inoculant.
  7. Grass with clover or lucerne – fermentation quality is the key. These silages are naturally more aerobically stable due to plant factors in combination with the silage fermentation inhibiting the yeasts and moulds. Homo-fermentative inoculant or chemical. Everytime.

Livestock-logoLivestock Event

This year’s Livestock Event taking place on 8 and 9 July at the NEC, Birmingham, includes a dedicated area called Forage Field, where visitors can find out all there is to know about making the most from forage. The event also has a Feed Science Forum covering topics such as feed efficiency and automated feed systems. Find out more about the event at