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Preservatives in round-bale silage
I have three years of research with wrapped bales for silage in Sweden and
Denmark. The problems you describe are not unique for New York, they also
occur here. Growth of molds and yeasts in the bales is always a result of air
leakage. Major contributing factors to air leakage are:
1. Too few layers of stretch film. We recommend no fewer than six layers of
25 to 30 um film. Consider that this only corresponds to 0.105 to 0.126 mm
plastic on the wrapped bale when the film has a prestretching of 70%.
2. Baling technique. Machine operators tend to drive too fast at baling,
resulting in unevenly shaped bales with low density. Low-density bales have
many air pores that are good distributors of air once air leaks into the
bale. Silage exceeding 40 to 45% dry matter are more prone to fungal growth
than silage of lower dry matter concentration.
3. Large differences in day and night temperatures result in different
pressures inside and outside the bale. The difference in pressure results in
gas exchanges, i.e. air being pumped inside the bales and carbon dioxide
being pumped out. This problem is reduced by selecting a shaded storage area
for the bales.
4. Holes in the plastic by birds and rodents. We recommend farmers to place a
net 20 inches above the bale surface as a protection from birds. Also, we
recommend placing rat poison on the ground. Further, the ground should be
well drained and free from tall growing vegetation.
5. The film is stretched excessively at wrapping. We recommend a 70%
prestretching of the film, i.e. the original film width of 500 mm is reduced
to 350 mm on the bale. The purpose of the prestretching is to get the plastic
tight to the bale surface and that it should stick better to the other
plastic layers. Excessively stretched film is wrinkled on the bales surface,
creating air channels. It is also more easily punctured.
6. Storage of bales for more than three months. Because wrapped bales have a
relatively large surface area exposed to air, prolonged storage should be
avoided.
Propionic acid is the most effective additive against fungal growth of which
I know. It is better to apply it before ensilage. Much higher doses of the
acid are required after fungal growth is detected. I have not seen any
studies where bacterial inoculants have had a greater effect on aerobic
stability.
All silage additives should be considered as preventative measures, and not
to solve problems after they have occurred. Thus, apply the additives before
ensilage.
I do not recommend feeding infested silage. Molds may contain toxins that are
potentially dangerous to animals. Further, molds may irritate the respiratory
system in both animal and man. The farmer should use a facial mask when
handling infested silage.
Christer Ohlsson
Senior scientist