Broschüre 2004 zum Download (pdf | 1994,28 KB) - H. Wilhelm ...

Figure 5: Concentration of BAB spores in samples taken from
the open front of grass and maize silages during feed-out
at a dairy farm. Multiple silages were fed during the
monitoring period (April 2003 to April 2004).
with results of earlier studies by Spoelstra et al. (4),
who found good correlations between BAB spores
and chemical parameters such as pH and ammonia-
N in laboratory-scale silages, but poor correlations in
farm-scale silages. Our hypothesis is that heterogeneity
of farm silages with respect to BAB concentration
plays an important role in these observations.
The importance of heterogeneity was confirmed by
analyses of silage clamps during the feed-out phase.
The BAB spore concentration of samples taken at
different time points after opening showed a large
variation, from about 10 2 /g to almost 10 7 /g (Figure
5). Surprisingly, this was observed not only for grass
Figure 6: Concentration of BAB spores in samples taken from the
surface layer and central area of the open front of maize
silage during feed-out at a dairy farm (front view).
silage but also for maize silage. Peak values occurred
even more frequently and were even higher in maize
silage than in grass silage.
Analysis of the distribution of the spores in opened
silages indicated that in many cases BAB spore
concentrations were significantly higher in the surface
layer than in the central area of the front. An
example of this phenomenon is depicted in Figure 6,
which shows the distribution of BAB spores in the
front side of a regular whole crop maize silage clamp.
High spore concentrations, up to 10 6 /g, were detected
at different positions in the surface layer. Further
research indicated that surface layers with high BAB
spore concentrations usually showed signs of aerobic
instability, i.e. a high pH and a high concentration of
yeasts and moulds.
Conclusions and discussion
The results of these investigations indicated that:
•
20 –25% of grass silages produced in 2002 and
2003 had a concentration of BAB spores higher
than 10 4 /g; the majority of these silages had a dry
matter concentration higher than 350 g/kg;
maize silage is an important source of BAB spores;
•
BAB spores accumulate in aerobically instable outer
layers and moulded spots.
An unexpected finding was that the occurrence of
high levels of BAB spores in Dutch silages seems to
be associated more often with aerobic instability problems
rather than with anaerobic instability problems.
Growth of clostridia, which are strictly anaerobic bacteria,
in aerobically instable surface layers may seem
a contradiction. However, though aerobic micro-organisms
dominate the microflora of these layers, it is
plausible that anaerobic micro-spots or niches occur
also. The rise in pH and temperature associated with
aerobic deterioration probably create environmental
conditions favourable to C. tyrobutyricum in these
niches.
The most likely causes for these problems are insufficient
consolidation and/or sealing of silages. It is
unknown why the problem hasn’t been recognized
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