Silage inoculants and corn silages:
Really a very interesting topic: . Very often producers affirm corn silages do not need a silage inoculant. This opinion is mainly based on the fact that corn silages show relatively high levels of acidity (low pH values) upon opening of the silo. This is due to the high amount of sugar in the material, the low buffer capacity and the relatively high epiphytic micro flora on the crop at harvest. However, it is very common to find aerobic instability in corn silages. Therefore we have two different topics to discuss: a) fermentation and b) aerobic stability.
a) Fermentation: The ensiling phase in which covered silages have higher losses is in the aerobic phase at the beginning. Depending on the compaction, lower or bigger amounts of oxygen remain inside the material and the endogenous enzymes are active. A sufficient decrease of the pH value is needed in order to stop the activity of the endogenous enzymes and prevent losses.
We cannot improve the compaction with a silage inoculant but it is possible to improve the acidification. In several laboratory trials using silage inoculants with different opening times we found that the acidification can be improved (faster and deeper) at the second day in case of corn silages. This could be the explanation why higher energy contents are found in corn silages at the opening of the silo.
b) Aerobic stability: it is generally recognized by the scientific community that aerobic instability is the main problem in corn silages. The use of silage inoculants with acetic or propionic acid producing strains can improve the shelf life of the silages. Nevertheless propionic acid producing bacteria live normally in higher pH conditions. Therefore the use of acetic acid producing bacteria is preferred.
Lactobacillus buchneri is doubtless the most known heterofermentative lactic acid bacterium (hLAB). However, other heLAB are available and produce a similar effect of improving the aerobic stability, for example, L. brevis or L. kefiri. Trials are available (see the proceedings of the last International Silage Conference (ISC) which took place in Madison, USA, in July 2009, for example). Compared with non treated silages Improvements in aerobic stability of 2 – 4 days have been found using products which contained these strains. It is desired to reach an acetic acid content of 1,5 – 3,0 [percent] in the DM in order to guarantee good aerobic stability but also a good palatability.
Homofermentative lactic acid bacteria (hoLAB ) produce mainly lactic acid, which is a good energy source for the growth of yeasts and moulds. Therefore no improvement in the aerobic stability should be expected when using silage inoculants containing only hoLAB.
Silages made, for example, of corn and grass are quite different. In the first case (corn silages), the emphasis should be placed on the aerobic stability. In the case of grass silages, an improvement in the fermentation. This is the reason why a differentiation in the product lines is needed.
Enzymes and corn silages: what is the aim?
Fibrolytic enzymes to breakdown complex carbohydrates into simple sugars for feeding the LAB? In corn harvested at a normal maturity stage there is enough sugar for the fermentation. The use of enzymes in general is controversial. The investigation done by the US researcher Kung (2002) about the use of enzymes in silages showed a low effectivity. Seven years later, Kung (ISC, 2009) named the results in the use of enzymes in silages as “inconsistent”. The pH value, for example, plays a role in the activity of the enzymes. Especially in corn silages, where the acidification is very quick and deep, most of the enzymes are out of their optimum pH range.
Yeasts as silage inoculants?:
Yeasts are present in the silages as sign of a bad sealing or spoilage in the feed out phase. Most yeast species require oxygen for their growth, however some of them are facultative anaerobes. Their main fermentation product is alcohol. Even more: they use the lactic acid for producing alcohol and other less desirable substances. Consequently, the silage quality, from all points of view (pH value, DM and energy losses, palatability), would be worse. Therefore their use as inoculant in the silage is not recommended.
Finally, we are completely agreed and it should be remarked that only good ensiling practices can be a guarantee for a successful inoculation and good silage quality. Silage inoculants work under proper conditions but they cannot replace good agricultural practices. It is not appropriate to recommend silage inoculants for correcting bad agricultural practices.