Introduction
The effectiveness of enzyme additives and their speed of action are influenced by:
Enzyme type and application rate: An enzyme’s effectiveness will increase with the quantity applied and its activity.
Unfortunately, the inclusion level or activity for enzymes in commercial additives is often not stated. This is exacerbated by the lack of a standardised method for measuring activity.
It is the cellulase, rather than the hemicellulase, portion of the enzyme additive that is most important and is likely to release most of the additional Water Soluble carbohydrates (WSCs) when an additive is used.
During a typical silage fermentation, the forage’s natural hemicellulase will degrade about 40% of the hemicellulose without extra activity from an enzyme additive.
Lactic acid bacteria (LAB): Not all homo-fermentative LAB can ferment the pentose sugars released by hemicellulases.
Mixed enzyme/inoculant additives containing hemicellulase should include LAB (Enterococcus, Pediococcus) that can utilise these sugars.
Forage type: Research with additives containing cellulases and hemicellulases has shown greater improvement in silage fermentation and greater reductions in fibre content (NDF and ADF), with immature grasses compared with more mature grasses, and with grasses compared with lucerne.
Improved responses with lucerne have been achieved by adding amylases and pectinases to the enzyme
mix. Temperature: Enzyme activity increases with temperature, although excessive heating in the silage stack or bale reduces enzyme activity.
Cellulases are generally active in the 20-50ºC temperature range, with optimum activity at the upper end of this range. pH: Cellulase activity is optimal at a pH of 4.5.
This is a disadvantage as optimum activity is not reached until the latter stages of the fermentation process.
However, the optimal pH can vary with cellulase source. Amylases generally reach optimum activity at pH 6.0, although some amylases will tolerate lower pH. DM content of the forage:
The activity of enzymes declines as forage DM increases. Because enzyme additives degrade the cell wall fraction in forages, resulting in increased effluent losses, enzyme application to low DM forages should be avoided.
There is evidence of reduced storage losses with wilted grasses and lucerne in the range 30-40% DM, when they are treated with enzymes.
The reduced losses are possibly due to improved compaction of treated forage, resulting in less air infiltration.
Time: Cellulases and hemicellulases are active over a prolonged period; but as indicated, their activity is related to pH.
The role for enzyme additives
In the past, enzyme additives have not been effective at the rates recommended. The application rates were too low to quickly release sufficient additional WSCs at the onset of silage fermentation to prevent poor fermentation of ‘at risk’, low DM forages.
In those circumstances, cost effective animal production did not occur. However, recent developments in biotechnology may improve enzyme efficacy and reduce the cost of enzyme treatments, allowing them to be used at higher rates.
