The composition of the ensiled forage and the subsequent fermentation will determine the type of silage produced. Silages produced under Australian conditions can be broadly classified into five main types:
Lactate silages
- Fermentation is dominated by Lactic Acid Bacteria (LAB);
- Water Soluble Carbohydrates (WSCs) are primarily converted to lactic acid;
- Have a pleasant, acidic and sometimes sweet smell;
- pH values are generally low (3.8-4.2), except in heavily wilted silages where the fermentation is restricted; and
- Contain high lactic acid levels relative to other organic acids.
Acetate silages
- Fermentation may be dominated by enterobacteria;
- More likely to occur when unwilted, or lightly wilted, low Dry Matter (DM) forage is ensiled;
- WSCs are primarily converted to acetic acid;
- Typified by a sour, vinegar smell;
- pH values are higher than those of lactate silages at the same DM content; and
- DM and energy losses can be significant.
Clostridial silages
- Fermentation is dominated by clostridia;
- More likely to occur when unwilted, or lightly wilted, low DM forage is ensiled;
- WSCs and lactic acid are converted to butyric and acetic acid;
- Characterised by low lactic acid levels and high pH;
- Proteins and amino acids are extensively degraded;
- Ammonia-N levels are high as a proportion of total N;
- DM and energy losses can be significant (silages are unpalatable to livestock and the utilisation of the N in these silages is poor); and
- Clostridial silages are not common in Australia.
Wilted silages
- Fermentation is dominated by LAB;
- Fermentation is restricted because of the high DM content (>30%). Less WSC are converted to lactic acid. pH values are higher than those of lactate silages;
- Residual, unfermented WSC levels can be high, but vary due to length and extent of wilting;
- Very dry forages are harder to compact, especially if chop length is long; there is a greater risk of yeast and mould growth because oxygen levels in the pit or bale are high in poorly compacted silages; and
- Higher residual WSC, poor compaction and carry-over yeast and mould spores can make these silages more aerobically unstable.
Silages with additives
The characteristics and type of fermentation observed varies with additive type.
