What happens in your silage after ensiling?

The pit is sealed, but the real work inside the silage is only just starting. Making silage means storing feed without air. Bacteria do the work, as long as you get the conditions right. What goes wrong in the first hours and weeks shows up months later at the feed barrier.

How is silage made?

Silage is forage stored with as little oxygen as possible, so that fermentation preserves the feed. The process has four phases:

1. Oxygen phase. Straight after sealing, the crop is still breathing. Together with micro-organisms, it uses up the last oxygen in the pit. This takes a few hours to a few days, depending on how well you compacted and covered. As long as there is oxygen, unwanted micro-organisms can grow.
2. Fermentation. Only when the oxygen has gone do lactic acid bacteria get to work. They turn sugars into lactic acid and other acids, such as acetic acid. This makes the pH drop.
3. Stable phase. Once the pH has dropped far enough, unwanted bacteria, yeasts and moulds are held back. More acetic acid forms, among other things, which makes the silage more stable. As long as no air or water gets in, the feed stays this good.
4. Feeding out. When you open the pit, oxygen reaches the feed again through the silage face. Yeasts can then become active again.

The faster the pit is free of oxygen, the more feed value you keep. That makes the first 24 to 48 hours after ensiling the most important. The whole chain from mowing to feeding is in the guide making and preserving silage.

What does oxygen do in the pit and why should it be sealed quickly?

Oxygen is the switch that starts heating. As soon as oxygen reaches the feed, yeasts become active. They break down sugars and lactic acid and turn them into heat. As the lactic acid disappears, the pH rises. Then moulds get a chance too, and they can produce mycotoxins.

The longer the pit stays open, the longer the oxygen phase lasts and the later fermentation starts. In a field trial with bales by Groeikracht, a Dutch silage advisory group, every hour of waiting before sealing cost about 1.5% extra dry matter. After 2.5 hours, more than 6% of the dry matter was lost (Veeteelt, May 2021). So cover the pit as soon as it is full. How to do that for each crop is in covering grass silage.

Oxygen gets in at three moments:

• During ensiling: through poor compaction. Put enough weight on the pit and compact the edges well too.
• During storage: through damaged plastic, badly sealed edges or a cover that doesn't fit tightly. Check the cover and repair damage straight away.
• During feeding out: through the silage face, especially if you pull the feed loose or the feed-out rate is low. Feed out at least 1.5 metres a week, and at least 2 metres in summer. More on this: the right feed-out rate.

Rainwater also disturbs the preservation: rainwater is much less acidic than good silage and slows down fermentation. Here is how to keep rainwater out of your silage. All tips against heating, during ensiling and feeding out, are in preventing silage heating. A covering system helps with some of these points, but no system is a miracle cure. Every step has to be right.

What dry matter content is good for preservation?

• Grass: aim for 35-45% dry matter. That material is the easiest to compact (Groeikracht).
• Forage maize: aim for 32-36% dry matter. Above 36%, the risk of heating and mould at feed-out increases (WUR, Handboek Snijmaïs).

Grass at around 40% dry matter is a good middle ground for most farms. A higher percentage only works if the material is chopped more finely, so you can still compact it enough. Also keep in mind that a longer wilting period in the field costs feed value.

What goes wrong if you ensile too wet?

If grass is too wet (below 30-35% dry matter), the pH drops too slowly. Water has a pH of 7 and slows down fermentation. This can lead to butyric acid.

What goes wrong if you ensile too dry?

At or above 50% dry matter, the material is often stemmy. It is hard to compact enough, more oxygen stays in and fermentation is slower. The silage becomes more prone to heating.

How long does silage need to ferment?

Keep the pit closed for at least 6 weeks before you start feeding. If you open it earlier, the pH hasn't dropped far enough and the feed isn't stable. With the oxygen that gets in, yeasts and moulds can grow quickly.

What pH does well-preserved silage have?

The pH is one signal alongside the other figures in your silage analysis. It depends on the dry matter and the type of silage. Wet grass silage (below 25% dry matter) is good at a pH of 3.8 to 4.2, and the drier the grass silage, the higher the pH can be (WUR, Handboek Melkveehouderij). Maize silage is usually at 4.0 to 4.2 (WUR, Handboek Snijmaïs). The limits for each dry matter level are in silage pH and fermentation.

A pH that is too high can occur in silage that is too dry as well as too wet. Then also look at the aerobic stability and the acids in your silage analysis. In maize silage, a higher pH can mean that oxygen was present for too long or that less lactic acid was formed.

What does poor preservation cost?

An example calculation from our brochure. A silage pit of 50 × 10 × 3 metres, with a small heap above the walls, holds about 1,750 m³ of grass silage. At 230 kg of dry matter per m³, that is 402,500 kg of dry matter. At a replacement value of €0.22 per kg of dry matter, that silage is worth €88,550 in feed value. Heating can easily cost an extra 10% in feed value (Silage Safe brochure, Eurofins Agro). That is €8,855. These figures are an indication only, not a guarantee. You'll find the full example in the brochure on our product information page.