Fütterungsbedingte mikrobielle Zusammensetzung von Rinderkot ...

5. Microbial biomass in faeces of dairy cows affected by a nitrogen deficient diet 48
In the current study, the concentration of microbial C, calculated on the basis of
bacterial muramic acid and fungal glucosamine was approximately 50% higher
compared with those in heifers (Jost et al., 2011). According to Amelung (2001, 2008),
the cell-wall components muramic acid and glucosamine have the tendency to be
accumulated in microbial residues, suggesting that roughly 75% of the faecal microbial
C in the present study belong to the living fraction and the other 25% are within the
remains of dead fungi and bacteria. In the highly dynamic situation of C and N supply
in the gut, rapid microbial growth is probably accompanied by concomitant microbial
death, as observed in soil (Chander and Joergensen, 2001). Although the current figures
seem to be realistic, they should be compared with other methods, because it is not
known (1) whether the glucosamine and muramic acid concentrations are identical in
living and dead microbial tissue and (2) whether the several conversion values for
microbial biomass C by the fumigation extraction method and for microbial C by amino
sugar analysis may lead to an underestimation of microbial biomass C. Furthermore,
this approach neglects the significant contribution of archaea to the faecal microbial
biomass, which contribute approximately 16% of the archaeal phospholipid etherlipid
(PLEL) to the total phospholipid chain content in cattle manure (Gattinger et al., 2007).
Archaea do not contain the amino sugar muramic acid (Kandler and König, 1998), but
most likely add to the CHCl3 labile C fraction obtained by the fumigation extraction
method.
In the context of the urea application in the N balanced diet, a decline was observed
in the microbial biomass C/N ratio and the fungal C to ergosterol ratio. The higher
supply of easily available N is expected to increase the N storage in faecal microbial
biomass, apparently accompanied by a shift within the fungal community. Potential
differences in microbial biomass content between the treatments were most likely
minimized due to higher N use efficiency with lower N availability from the diet (Bach
et al., 2005; Calsamiglia et al., 2010).
5.4.2. Bacterial and fungal contribution to microbial tissue
The average fungal C to bacterial C ratio of 0.34 found in this study is in line with
the assumption of 25% fungal C and 75% bacterial C. This means that the faeces of
dairy cows contained considerably less fungal C than faeces of heifers, where fungi