Successful Silage – II
What Are Aerobic Spoilage Inhibitors?
Frank Mickan, DPI Ellinbank
The many years of research into silage additives has resulted in many thoroughly researched and robust products available on the market worldwide. These have been confidently used in Europe, United Kingdom and USA for many years and are now viewed as another step towards ensuring silage undergoes a satisfactory fermentation. It is only in recent years that some Australian farmers and many professional contractors have started to use additives regularly,
although some are still sceptical.
There are three main types of silage additives:
Fermentation enhancers or stimulants: (inoculants, enzymes and sugars) promote more rapid fermentation and consequently a faster drop in pH levels (i.e. increased acidity), which helps to preserve the crop more quickly, reducing dry matter and quality losses.
Anaerobic1 fermentation inhibitors: (organic acids, buffered acids, specific sulphur-bearing compounds + amylase2) reduce or prevent fermentation by naturally occurring bacterial groups in the forage.
Aerobic3 spoilage inhibitors: (organic acids, buffered acids, special purpose inoculants, nonprotein nitrogen, sulphur-bearing compounds + amylase) delay the onset of silage spoilage (through heating, yeast and mould growth) by substantially slowing the effects of air entering the silage upon opening of the stack.
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Figure 4: Steam and mould caused by aerobic spoilage |
This article will discuss aerobic spoilage inhibitors. Aerobic spoilage is the spoilage of silage by undesirable microorganisms (i.e. yeast, mould and bacteria), upon exposure of the silage to oxygen at feed out. Once the silage is exposed to oxygen, carbon dioxide, heat and water are produced and mould growth develops.
In the past, particularly in Europe and the United Kingdom, acids and buffered acids (a safer option which are much more user friendly to man and equipment), have been very successful in reducing aerobic spoilage at feed out. However, other types of additives have come onto the market in recent years to do the same job using different modes of action.
Why the need for aerobic spoilage inhibitors? Once most silage stacks are open to the air at feed out, the dormant ‘undesirable’ microorganisms (yeasts, mould spores and acetic acid producing bacteria) ‘wake up’ and start consuming the residual plant sugars and the lactic acid produced by the favourable bacteria when the fodder was first ensiled. The build up of the undesirable microorganisms during ensiling is kept low if the ensiling process was rapid at harvest, contained plants of high sugar contents, was well-rolled and sealed airtight soon after harvest.
If however, only ONE of these ensiling management practices was less than ideal, such as large quantities of air being trapped in the stack due to poor compaction (see Figure 3), the undesirable microorganisms will use the available oxygen to greatly increase in number and will then become dormant. The mould then forms spores over the storage period.
1 Anaerobic: requiring, living in, or caused by the absence of oxygen
2 Amylase: enzyme that catalyses the breakdown of starch into sugars
3 Aerobic: requiring, living in, or caused by the presence of oxygen
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Figure 3: Poor compaction |
Upon opening the silage, their already large populations of microorganisms increase very quickly, consuming the residual sugars and breaking down the lactic acid. The result of which is carbon dioxide (not visible), heat and water (seen as steam arising from the stack or moisture under the plastic sheet) and mould growth (see Figure 4 – mould and steam in maize silage). The activity of the undesirable microorganisms also results in large losses of dry matter and energy, and the breakdown of the true protein into lesser products.
A recent advance in controlling aerobic spoilage is a bacterial inoculant containing Lactobacillus buchneri 40788. The ‘40788’ refers to a specific strain of L. buchneri, which has been shown to be most effective in doing the job. It is still unclear as to how it completely achieves the end result of delayed aerobic spoilage deterioration, but it is known to break down some of the lactic acid into acetic acid, which in turn inhibits yeast growth, the main culprits in stack heating and subsequent mould growth.
This bacteria on its own and sometimes mixed with other bacteria, will usually delay the onset of aerobic spoilage. It is applied at ensiling, as are other inoculants, but works best if well established, good ensiling practices are followed. L. buchneri will not prevent silage spoilage deterioration in stacks where the plastic has had holes in it for many days.
The L. buchneri inoculant is particularly useful in maize and whole crop cereal silages cut at the soft dough stage. It is useful in silage stacks where the feeding face is too wide for the feed out rate and farmers will know this by the presence of heat and mould in previous years. I’m not advocating this, but L. buchneri may cover up poor face management, such as a loose face silage left at the stack base or where silage is left in a TMR overnight. However, the effective period of delayed spoilage achievable from using L. buchneri will be substantially reduced compared to well-managed silage operations, due to the increased exposure to oxygen.
Another product that contains sulphur compounds and amylase is a fermentation inhibitor that also has the effect of being an aerobic spoilage inhibitor at feed out. There are other products purporting to act as aerobic inhibitors that may or may not work. It is best to ask the product salesman to provide independent research to back up the claims made. If you are convinced to buy the product you can test its effectiveness at feed out. There should be no heating or mould growth for at least two to three days after opening, if not longer.
Aerobic spoilage can cause a significant reduction in the dry matter and energy content of the silage. This can be delayed and reduced with the use of aerobic spoilage inhibitors. However, aerobic spoilage inhibitors are not a substitute for good ensiling practices, which should always be followed regardless, to ensure an optimum product at feed out.
