Forage Harvester
Introduction
An acid fermentation occurs when forages of sufficiently high moisture content are stored under anaerobic conditions.
During fermentation, bacteria convert plant sugars, Water Soluble Carbohydrates (WSCs), to fermentation acids and other compounds.
Ideally, this fermentation produces mainly lactic acid and in sufficient quantity to quickly reduce pH.
At low pH, acid conditions prevent further microbial activity and spoilage. The final pH achieved in a well-preserved silage depends on the WSC and dry matter (DM) content of the forage at time of ensiling. The final pH may be as low as 3.8-4.2, but could exceed 5.0 in heavily wilted silages, particularly those produced from legumes.
The silage will not deteriorate as long as anaerobic conditions are maintained. In other words, the nutrients in the silage are preserved while the silo or bale remains sealed. The rate and efficiency of the fermentation process, the products of fermentation, and the fermentation quality of the resulting silage depend on several factors, the most important being the composition of the parent material at the time of ensiling and the species of bacteria that dominate the fermentation.
The quality of the silage produced depends on its nutritive value – digestibility, ME, protein and mineral content – combined with its fermentation quality (see Figure 2.1). Poorly fermented silage may result in inferior animal production due to unpalatability and poor utilisation of dietary nitrogen (crude protein).
Losses in quality can occur throughout the silage-making process. The level of loss will depend on:
- The physical and chemical properties of the forage at the time of harvest and ensiling;
- Wilting conditions and the extent of wilting;
- The harvesting process;
- The efficiency of the fermentation
- Process;
- Maintenance of anaerobic conditions during storage; and
- Management during feedout.
The composition of the parent forage at ensiling has a major influence on the silage fermentation. The most important components are DM content, WSC content and buffering capacity (BC).
Dry matter content The DM content of the parent forage at ensiling can affect the quantity of effluent lost from the silage during storage, the growth of bacteria in the silage and the ease of compaction which, in turn, affects the exclusion of air from the silo or bale.
Effluent
During the early stages of the ensiling process, as the cell structure breaks down due to compaction and the action of plant enzymes and microbial activity, fluids are released from within the cells. If the forage is stored at low DM content – in particular unwilted, direct-cut pastures or forages containing ‘free’ water from rainfall or dew – surplus moisture (including soluble compounds) will flow out of the silo as silage effluent.
The quantity of effluent produced is directly related to the DM content of the forage ensiled and the extent of compaction of the silage. Effluent flow falls as DM content increases (see Figure 2.2), and stops when the DM content reaches about 30%. As a result, wilting is an effective management strategy for reducing effluent losses.
Effluent flow is slightly greater for finer chopped compared to long chop forage. Silage effluent contains Water Soluble Carbohydrates WSCs, protein, minerals and fermentation products, so it represents a significant loss of nutrients.
