Mould in silage: 4 causes and how to prevent it

A white or blue-green layer at the top or along the wall: you can throw that feed away. Mould in silage costs feed value and palatability, and it can be toxic to your livestock. Once the mould is there, it is hard to get rid of. So tackle the 4 main causes before it gets that far.

Why is mould in silage a problem?

Mould lowers the feed value and cows are less keen to eat the silage. Some moulds produce toxins. That has a direct effect on the health and production of your livestock. Moulds need oxygen and grow fastest where the pH is high. So wherever air or water gets into the silage, they get a chance.

How does mould get into silage? 4 causes

Cause 1: poor compaction

If the silage isn't compacted well, oxygen stays behind in the pit. That oxygen helps moulds grow and increases the risk of spoilage. When feeding out, air also penetrates further into the silage face.

How to prevent it:

1. Ensile in thin layers. Thin layers are easier to compact.
2. Roll without dual wheels and avoid ruts. Dual wheels reduce the pressure per cm².
3. Keep the incoming material and the weight on the pit in balance. Put at least half the weight of the fresh material coming in per hour on the pit. If 30 tonnes per hour comes in, at least 15 tonnes should be rolling the pit.

You can read more in 6 tips for good silage compaction.

Cause 2: a cover that lets air or water in

With a poor cover, fresh oxygen keeps reaching the feed. Rainwater that runs in raises the pH. That gives moulds exactly what they need.

How to prevent it:

1. Don't skimp on plastic. Choose a good underlay film and top sheet that let little oxygen through and don't tear easily. An underlay with an oxygen barrier lets far less air through.
2. Keep enough pressure behind the silage face. That is where wind can get under the plastic. Moulds then get a chance further into the pit. How to keep the plastic in place in strong wind is explained in covering silage in strong wind.
3. Repair holes and tears straight away. Check the cover regularly, for example for holes caused by pests at your silage pit, and tape them up immediately.

How to keep water out of the silage is explained in preventing rainwater in silage.

Cause 3: a feed-out rate that is too low

With a feed-out rate that is too low, the silage face is open for too long. The feed warms up and becomes less palatable. Heat, oxygen and water together are the ideal conditions for bacteria and moulds. That is why mould and heating in silage often go together.

How to prevent it:

1. Match the height of the pit to what you feed. Several smaller pits are better than one very large one, because then you feed out faster. We advise at least 1.5 metres per week in winter and 2 metres in summer.
2. Keep the silage face smooth and even. Less water and oxygen get in.

How to work out your feed-out rate is explained in the right feed-out rate.

Cause 4: poor hygiene

Dirty machines, a dirty silage pit or loose silage in front of the face are breeding grounds for bacteria and moulds. They contaminate the silage through direct contact, the air or water.

How to prevent it:

1. Don't use old silage plastic. It carries bacteria and moulds.
2. Work cleanly when ensiling. Make sure the silage pit and the access route are clean. Make sure tractor tyres are clean before they drive onto the pit with fresh material. That way you don't ensile extra bacteria and moulds.
3. Don't leave loose feed or dirt in front of the silage face. Bacteria and moulds grow quickly there and contaminate the face.
4. Keep pests away. Pests eat holes in the cover and spread bacteria, moulds and other pathogens with their droppings.

Soil on the pit also brings dirt into the feed. Andre Schulte from Denekamp in the Netherlands stopped using it: "Because we no longer use soil, the risk of butyric acid and listeria bacteria is much lower."

Why is the mould mainly at the top and at the edges?

That is where the silage is hardest to compact well, so that is where most of the air is. Tyres and soil don't stay in place well at the edges. And rainwater that runs into the silage along the sides raises the pH there. Yeasts and moulds then survive, and as soon as oxygen gets in again, they strike. So the cover must fit tightly and apply pressure, especially at the edges.

Wiljan Ten Hove from Kamperveen in the Netherlands saw it on his own farm for years: heating and mould regularly appeared along the walls. Since he started covering his five pits with Silage Safe, the system seals the pit airtight and he has hardly had any trouble with it. See how the covers keep pressure on the edges and drain away rainwater on our product information page.

Checklist: from covering to feeding out

Mould usually comes from a combination of small things. Check these points regularly:

• Plastic: are there holes or tears? Tape them up straight away.
• On top of the pit: is water standing on it? Then the pit isn't nicely rounded.
• Edges: does the cover fit tightly against the wall?
• Silage face: is it tight and cool, and is there enough pressure behind the face?
• In front of the face: is there loose feed or dirt? Remove it.
• Feed-out rate: do you reach at least 1.5 metres per week in winter and 2 metres in summer?