Aerobic spoilage refers to the deterioration of silage when oxygen enters the clamp, either during storage (due to poor sealing) or feed-out (when the silage is exposed to air). It is one of the most significant contributors to dry matter and nutrient losses, particularly in both grass and maize silage.
What Causes It?
When oxygen becomes available, yeasts and moulds multiply rapidly. These microorganisms consume nutrients in the silage—particularly lactic acid and sugars—for their own metabolism, converting them into carbon dioxide, water, and heat. This process raises the temperature of the silage and triggers a chain reaction of spoilage.
Key causes:
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Poor compaction
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Delayed or damaged sealing
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Slow feed-out rate
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Reheating at the clamp face
The True Loss: Beyond Just Dry Matter
The visible spoilage (mouldy, discoloured, hot or slimy silage) is only the tip of the iceberg. The real damage includes:
1. Loss of Energy and Nutrients
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Yeasts consume water-soluble carbohydrates (sugars), reducing metabolisable energy.
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Moulds can degrade proteins, lowering the crude protein content.
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Lactic acid, vital for preservation, is broken down, destabilising the pH.
2. Increased Dry Matter Losses
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Aerobic spoilage alone can cause 5–20% DM loss, depending on conditions.
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Maize silage, with its high sugar content, is more prone to aerobic deterioration than grass silage.
3. Reduced Animal Performance
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Spoiled silage is less palatable.
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Livestock may reduce intake, impacting milk yield and weight gain.
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Contaminated silage increases the risk of mycotoxins, which may cause health problems.
4. Heat Production = Invisible Loss
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The heat generated during spoilage is not just inconvenient—it represents a loss of energy that could otherwise support growth or milk production.
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A 10°C increase in silage temperature can lead to a loss of up to 4% of the energy in that portion.
5. Labour and Waste Handling Costs
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Spoiled silage often needs to be removed and disposed of.
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This results in additional labour, higher disposal costs, and potentially reduced forage stocks earlier than expected.
How to Minimise Aerobic Spoilage
✅ Compact thoroughly: Aim for at least 240 kg of DM/m³ to limit oxygen penetration.
✅ Seal immediately: Use high-quality plastic sheeting and weigh it down properly.
✅ Use silage additives: Inoculants containing Lactobacillus buchneri can help stabilise silage when exposed to air.
✅ Fast feed-out: Aim to remove at least 15–30 cm per day from the clamp face.
✅ Maintain a clean, tight face: Smooth the face daily to prevent oxygen ingress.
