Ensiling is a forage preservation method based on a lactic acid fermentation under anaerobic conditions. Homofermenting lactic acid bacteria ferment the water-soluble carbohydrates (sugars) present in the crop to lactic acid, a strong organic acid, thus lowering the pH. By lowering the pH to a level where unwanted micro-organisms cannot proliferate, losses in dry matter are reduced, preserving the energy value of the silage.
There are four phases to the ensiling process, which begin as soon as the crop is cut:
- Aerobic
- Fermentation (anaerobic)
- Stable
- Feed-out
Aerobic phase
- This phase lasts until all oxygen is used up.
- It is the final stages of respiration, which began once the crop was harvested.
- Plant enzyme activity will continue while oxygen is present.
Fermentation phase
- This begins once the oxygen in the silage clamp has been used up – it occurs in anaerobic conditions.
- Can last several weeks – but a faster fermentation is desired.
- Lactic acid dominates in a good fermentation.
- Ph drops to 3.7 – 4.5
Stable phase
- Acidic conditions limit microbial activity providing the clamp is airtight and a stable, low pH has been achieved.
- Micro-organism populations gradually decline although some microbes can remain active if the pH is not low enough.
- Yeasts become dormant, and unwanted clostridia, bacilli, and moulds can survive as spores, ready to develop if conditions are suitable for them.
Feed-out phase
- Aerobic spoilage will start on exposure to air.
- Any dormant yeasts and mould spores, now in the presence of air, are able to degrade the available lactic acid and plant sugars.
- Heat is generated as carbon dioxide and water are produced – this is DRY MATTER LOSS. A clamp is considered to be unstable when the temperature has risen by 30C.
- Moulds begin to grow and can produce harmful mycotoxins.
- Dry matter losses can be significant in this stage.
Dry matter losses can be considerably reduced by treating your forage crop with the correct additive.