Sugar content of grass: why it matters for ensiling

Sugar in grass is the fuel for your grass silage. If there is too little, the silage ferments poorly and the feed is less palatable. How much sugar you get into the pit depends largely on the weather, the moment you mow and how quickly you seal.

Why is sugar important for your grass silage?

During preservation, bacteria turn the sugars in the grass into lactic acid and acetic acid. These acids make the pH of the silage drop. That gives unwanted bacteria, moulds and yeasts less chance and keeps the feed good. Together with the remaining sugars, the acids also make the feed palatable for your cows. How this works exactly is in silage pH and fermentation.

When in the day does grass contain the most sugar?

Sugar content rises during the day, especially in sunny weather. The difference between morning and evening can be 35 to 50 grams of sugar in the fresh crop (WUR). So it is better to mow later in the day than early in the morning. WUR advises mowing in the middle of the day, once the dew is off. Then the grass can still wilt to about 30% dry matter by evening, and less is lost overnight.

What happens with a low sugar content?

With little sugar, the bacteria form less lactic acid and acetic acid. The silage then ferments more slowly and less well. The feed preserves worse and is less palatable. Cows eat less of it, and that costs production. Silage that doesn't ferment well also gives butyric acid bacteria more chance.

Why does sugar content vary by cut and by year?

Sugar and protein often move in opposite directions. Silage analyses show that one summer gives a high sugar content with little protein, while in another period fresh grass has a lot of protein and little sugar. That depends on the weather and on fertilising:

• Sun: grass makes sugar in the sun. The more sun, the more sugar.
• Cold nights: at night, grass turns sugar into plant material. The colder the night, the less this happens. That is why sugar content can rise sharply, especially in spring.
• Nitrogen: the more nitrogen the soil supplies or the more heavily you fertilise, the higher the protein and the lower the sugar (WUR).

How do you keep more sugar in your silage? 4 tips

1. Mow after a few sunny days. Then the grass has built up sugar.
2. Mow later in the day, not early in the morning. The middle of the day, once the dew is off, works best.
3. Keep the wilting period short. The shorter the grass lies in the field, the more sugar is left. In dull weather, or if the grass isn't properly wilted when it goes into the pit, a lot of sugar is lost after mowing. Preferably ensile before the next evening.
4. Seal straight away. As long as the pit is open, sugars are lost instead of becoming lactic acid. Quick, airtight covering gets fermentation going straight away. The approach is in covering grass silage. See how quickly you can seal the pit with Silage Safe on our product information page.

What you keep in the pit, you will see in what your cows eat. "We can now retain much more of the protein in our grass silage," says Jarne Schuiling from Vries.

Keep in mind: the sugar content of fresh grass doesn't tell you everything about the silage. How quickly the grass wilts and how quickly the silage starts to ferment decide how much sugar really ends up as lactic acid. More tips for spring are in first cut silage tips, and the whole chain from soil to covering is in improving silage quality.