Does baled grass silage need an additive?

With baled silage, fermentation is slower and restricted due to the longer chop length and the typically higher % dry matter (DM) of the grass. There can also be a lot of variability between individual bales, especially if the grass sward varies across the field. In a clamp, such variability gets evened out to a large extent.

Bales are also more susceptible to aerobic spoilage (heating and moulding) due to their high %DM and large surface area to volume ratio making air removal more difficult – 27% of the volume of a 4 foot bale is in the outer 5 cm. They are also less dense compared to clamped silage, although improvements in balers have meant densities have been much increased over the years.

Another issue with bales is their susceptibility to the growth of Listeria bacteria due to their higher pH and increased risk of aerobic spoilage. Listeria only needs a small amount of air ingress – e.g. from pierced wrap – to be able to grow.

Bales can therefore benefit greatly from an additive that will improve fermentation and reduce aerobic spoilage.

What type of additive should be used on baled grass silage?

The specific additive used can be tailored to the % DM of the bales and how long the silage will be exposed to air for once opened before being consumed.

For lower %DM bales (e.g. below 33% DM) that will be eaten within a day (e.g. on dairy farms) and where there is little risk of aerobic spoilage, then focus on an additive that preserves the bale by improving the initial fermentation e.g. Ecosyl 100.

If bales are likely to be open for two or three days before being eaten (e.g. on beef and sheep units) then focus on the initial fermentation but also on tackling spoilage and heating risks. For example, consider Ecocool, which contains two beneficial bacterial strains, one for fermentation and one to target the yeasts and moulds that cause heating and spoilage. Alternatively, consider Double Action (DA) Ecobale, which includes two bacteria, one of which is effective at fermenting drier material, plus a feed-approved preservative.

What colour of wrap should be used on baled grass silage?

When black plastic is warmed by the sun it absorbs much of the heat and becomes more permeable to oxygen, and the outer layer of forage also warms up. White plastic reflects more of the sunlight which reduces the activities of spoilage microorganisms in the bale. Green plastic is intermediate between black and white.

Reflection and surface temperature with different colours of bale wrap (six layers)
A 20^oC increase in temperature can increase wrap permeability by 300%

	Black	Dark green	Light green	White
Reflection (%)	4	13	28	31
Surface temperature (oC)	53	46	35	32

SLU, Uppsala, Sweden

How many layers of wrap should be used on baled grass silage?

More layers reduces oxygen permeability and the risk of damage to the wrap. A minimum of four layers (50% overlap) is essential but increasing to six is beneficial as it provides a better oxygen barrier. Some work at CEDAR with black wrap found that 10% dry matter (DM) losses with four layers were reduced to just 1% by using six layers, and the silage also had a better feed value. More layers should also be used with more mature or stalky forages, and very high %DM grass – e.g. haylage – as well as with square bales.

Consideration should be given to the responsible disposal of plastic wrap.

	Minimum number of layers
Round bales <40% DM	4
Round bales 40-50% DM	6
Square bales <50% DM	6
>50% DM or stalky	8

How should grass silage bales be stored?

Store bales in a dry, sheltered area preferably on a prepared base. They should not be overhung by trees and should be at least 10 metres from a water course, ditch or field drain.

Stack height depends on the dry matter (DM) of the silage. Bales made of lush, leafy grass should not be stacked at all. If the DM is 25-35% they can be stacked two high and if more than 35% they can be stacked three or four high. Stacking them on their ends is another option as the ends have more wrap layers over them so provide extra protection, but they tend to be less stable so cannot be stacked so high.

Stack within 24 hours of wrapping and do not disturb them again for at least three weeks if possible.

If concerned about vermin damage bait the area around the stack – not within the stack. This should start a few months before you are likely to stack bales. 

If birds are a problem it would be wise to net the stack. Some people say that mounting a plastic bird-of-prey is also very effective. Also, make sure to protect the stack from the attentions of livestock.

Inspect the bales for damage regularly and seal any holes. If still suitable, use those bales first.

What are possible reasons for grass silage bales being mouldy on opening?

Moulds can only grow in the presence of air, so if bales are mouldy when opened it is an indicator that air has been available to them.

There are a number of potential reasons for this:

• Delayed wrapping
• Air pockets under the wrap – e.g. due to misshapen bales are badly-wrapped bales
• Poor wrapping
• Not enough layers of wrap
• Poor quality wrap allowing air to infiltrate slowly
• Damage to the wrap
• Degradation of the wrap – e.g. old bales exposed to the elements
• Suitable additive not used

No additive will be able to prevent bales going mouldy if they are exposed to air for a long period.

Why are grass silage bales more likely to go mouldy?

The grass in bales is not so highly compacted as in a clamp and is not chopped as short. 

These factors, together with the fact that the grass for bales normally has a high % dry matter content, mean that more air is trapped in the bale initially, allowing the yeasts that initiate aerobic spoilage a longer period to grow and multiply before the air gets used up. 

This means higher numbers of yeasts present later if air should get in, so spoilage will begin faster. Bales also have a high surface area to volume ratio which means a greater area is potentially exposed to air.

How to calculate how much silage is in bales?

Weigh a few bales or estimate their weight then calculate your total fresh weight baled silage stocks. Carry out an oven % dry matter (%DM) test on samples from several bales as described in the clamped silage section, then calculate DM stocks as follows:

Tonnes DM = tonnes fresh weight x %DM ÷ 100