How to make good silage

Making high quality, well preserved silage enables the AD to store quality forage as feedstock, providing a cost effective feed when required. The challenge is to ensure that energy in the form of valuable sugar, starch and soluble proteins are protected from being lost to aerobic breakdown by yeasts and mould.

An effective silage additive helps to drive fermentation in the right direction, preventing undesirable yeasts and mould from depleting valuable energy and protein resources from the ensiled forage. Dry matter energy losses leaves a higher concentration of lower-value nutrients, like fibre and ash.

Following best practice at every stage of the process – from harvesting to ensiling to feeding out – will ensure you get the highest gas yield from your silage.

Top tips for good silage

Harvest your crop at the ideal stage of growth to maximise energy content and optimise dry matter yield. Maize is best at 32-36% DM.
Determine key chop length at harvest to suit dry matter content. The drier the material, the shorted the chop length. Maize is ideal at 4-6mm.
Fill the clamp to maximise anaerobic conditions by aligning harvest rate to clamp filling speed (tractor deliveries and compaction times).
Compaction – This is a critical element. If not compacted well, yeast and mycotoxin formation in “air” pockets will develop and spread. Compaction should be done systematically in 15-20cm layers. (700-750kg/ m3 FW).
Complete the ensiling process as quickly as possible (ideally within 24hrs). The longer the silage is exposed to air, the more oxygen will ingress in-to the compacted silage, causing yeast and mould counts to rise, thereby increasing the risk of spoilage at feed out).
Sheeting – Cover the clamp immediately and use dedicated oxygen barrier films to create anaerobic conditions as fast as possible. Ensure a 1m overlap between sheet sides.
Feed out - Adequate speed of progression in feeding out from the clamp at a maximum of 7 days clamp face exposure. We recommend a minimum of a metre/week along the entire length of the clamp face to keep heating and the associated energy loss to a minimum. The longer the face is exposed, the more yeast and mould will grow causing secondary heating and losses, evident by increased silage temperature. Keep the cut face tight, clean and surface area to a minimum.

Types of silage additives

Biological additives

Bacteria only based additives

The majority of biological silage inoculants are based on lactic acid bacteria (LAB). Some products contain only homofermentative strains, only heterofermentative strains, or a combination of both.

Homofermentative bacteria such as Lactobacillus plantarum, Lactocbacillus Rhamnosus, Lactobacillus pracasei enhance the production of lactic acid, leading to a faster drop in pH value and improved fermentation, thus reducing DM losses, protein breakdown and growth of undesirable microorganisms. They ferment glucose to lactic acid, pentoses and gluconate.

Heterofermentative bacteria such as Lactobacillus diolvorans, Lactobacillus buchneri and L. kefiri convert forage sugars to lactic and acetic acid. The production of acetic acid will improve aerobic stability of the silage by preventing proliferation of undesirable yeast and mould keeping silage highly nutrient, hygienic and most importantly, stable and at a reduced risk of spoilage.

Glucose und Fructose are converted to lactic acid, ethanol, acetic acid, mannitol and 1,2-propandiol.

Due to its high buffer capacity in grass silage, the main challenge is to achieve fast acidification, i.e pH-drop. A homofermentative silage additive will yield high concentrations of lactic acid, ensuring rapid decrease of pH and clamp stability.

A combination of homo- and heterofermentative lactic acid bacteria guarantees not only optimal fermentation but also enhanced aerobic stability.

Combination biological additives

Enzyme + Bacteria

The aim of adding enzymes to silage is usually to aid the breakdown of plant cell walls (e.g. use of celluloses and hemi-celluloses). The main benefit of this appears to be an increase in the amount of sugars available for LAB bacteria to convert to lactic acid for more rapid acidification.

While there is some evidence of favourable outcomes of this on silage quality and animal production, there is very little evidence suggesting that the enzymes will have a positive impact in aiding the Bio-methane yield.

An additive with enzyme is not cost effective and the effect of the enzymes is negligible due to the abundance of free sugars in silage to create good fermentation. Biogas plants have a typically good retention time, therefore the “supposed” benefit of increasing digestibility in the AD is not realistic as the quantity of enzyme required would need to be at a much higher concentration.

The below independent study demonstrates that at 49 days with aerobic stress, (typical on site AD clamp) an additive that combines bacteria and enzymes, LAB-he A (Lactobacillus buchneri + Apergillus oryzae β-glucanase and α-amylase, Trichoderma longibrachiatum xylanase) was unable to produce significant positive results in bio-methane production and reduce dry matter losses when compared to biological additives with homo and hetero fermentative lactic acid bacteria.

“…LAB-ho+he B (Silasil Energy) were effective to completely avoid aerobic deterioration during 7 days exposure to air…”

“…Highest methane yields were analysed with addition of LAB-ho+he B. Under air stress conditions, treatment of maize with the inoculant LAB-ho+he B significantly increased the methane yield…”

Dr Pat Hoffman and Dr Richard Muck of the USDA Forage Research Centre have stated, “Enzymes can improve silage fermentation when the substrate (e.g., sugars) is limiting. Soluble sugars are required to help bacteria produce lactic acid, which is required to lower silage pH for proper fermentation. Generally, enzyme addition to silages has a small effect on fermentation.”

If a product claims to contain enzymes, the label should clearly state guaranteed levels. It’s not enough to simply list some enzyme sources in the ingredients. Without guaranteed levels, you can assume that any enzyme activity present is limited at best. To be effective, a product must contain guaranteed levels that are validated effective by research studies.

Chemical preservatives and organic acid additives

The use of organic acids such as propionic acids are aimed at lowering the silage pH to make it less favourable for undesirable bacteria such as Clostridia. Other chemical preservatives and their salts including potassium sorbate, sodium benzoate and sulphiting compounds, target the growth of yeasts and mould fungi either in fermentation or during feed out.

There needs to be sufficient amount of the additive to provide a concentration in the bulk forage that will actually have a sufficient effect on the growth of those undesirable organisms. That rate is typically at 4.5 lts of active ingredient per tonne of forage to preserve the silage. Compare those values to what is actually contained in a product claiming a preserving affect.

At the lower inclusion rate (less than 4.5 Lt/ton of active ingredient), preservatives do not provide full stability and preservation. To ensure adequate fermentation it is advisable to use silage inoculants. Bear in mind that organic acids and chemicals cannot be mixed together with biological silage additives.

When looked at from an economic standpoint, lactic acid bacteria are more cost effective and are able to produce more energetic compounds such as acetic acid (fast production of biogas) and propylene glycol.

The below independent study demonstrates that at 49days with aerobic stress, (typical on site AD clamp) 4.5lt/t of chemical additive was able to produce positive results that lead to an increase in bio-methane production and reduced dry matter losses. The results were very close to what is attained by a biological additive that has Homo and Hetero fermentative lactic acid bacteria. (LAB-ho+he B)

“…a 3% higher methane yield was found for silages treated with chemical additive, and 4-9% higher methane yields were found for silages treated with homo and hetero fermentative LAB…”

Common mycotoxin-producing molds in forage

Penicillium roqueforti
White mycelium with blue green to green when producing spores. The major occurence is in maize, grass and wholecrop silage.

Monascus ruber
White mycelium with yellow-orange to mostly red when mature. The major occurence is in maize silage.

Aspergillus fumigatus
White mycelium with cream to bluish-grey to dark brown when producing spores, some types remain white. The major occurence is in maize, grass and wholecrop silage. Trypacidin: Poses pulmonary mycosis health risk to people – avoid spore inhalation.

Aspergillus ochraceus
White mycelium, spore production is chalky yellow to pale yellow brown. The major occurence is in maize, grass and wholecrop silage.

Aspergillus flavus
Dryed out areas, white mycelium, spore production is usually yellow/green turning dark green but can be white. The major occurence is in maize silage.

Penicillium spp.
White mycelium, green-blue to dark grey when producing spores. The major occurence is in maize, grass and grain silage.

Fusarium spp.