Fütterungsbedingte mikrobielle Zusammensetzung von Rinderkot ...

5. Microbial biomass in faeces of dairy cows affected by a nitrogen deficient diet 49
contributed more than 40% to microbial C (Jost et al., 2011). This difference is due to
the higher content of structural components such as ADF in the heifer diet.
Chitin, the polymer of glucosamine, has previously been used as an indicator of
fungal biomass in rumen fluid of cattle (Sekhavati et al., 2009) and in sheep faeces
(Rezaeian et al., 2004a, b). The chitin concentration in sheep faeces was 10.2 mg g -1
DM (Rezaeian et al., 2004a). In a sheep feeding experiment, the liquid associated
fraction of rumen material contained 12.1 to 15.4 mg chitin g -1 DM and in the
corresponding particle associated fraction 2.6 to 3.9 mg chitin g -1 DM. One reason for
the markedly higher chitin concentration compared with the glucosamine concentration
in the present study might be the differences in rumen and intestine physiology between
sheep and cattle. However, Rezaeian et al. (2004a, 2006) used the colorimetric assay of
Chen and Johnson (1983), which cannot distinguish between fungal glucosamine,
bacterial glucosamine, and galactosamine. This may lead to an overestimation of fungal
tissue. In accordance with the present data, Rezaeian et al. (2004a) have estimated that
anaerobic fungi comprise approximately 20% of the total microbial biomass in the
rumen of sheep.
In the current study, the mean faecal concentration of ergosterol was 13.2 µg g -1
DM. Klamer and Bååth (2004) obtained a factor of 190 when calculating the fungal
biomass C from the ergosterol concentration in 11 compost fungi species. Taking this
factor into account would result in a mean fungal biomass C content of 2.5 mg C g -1
DM in the present faeces samples, suggesting that ergosterol containing fungi contribute
a proportion of 7% to the total microbial biomass in both treatments.
Ergosterol has been repeatedly used as an index for fungal biomass in soil (Bååth
and Anderson, 2003) and other solid substrates (Newell, 1992), but only once in cattle
faeces (Jost et al., 2011). Of the anaerobic fungal populations, yeasts such as Candida
sp. (Ahmad et al., 2010) or Saccharomyces cerevisia (Aguilera et al., 2006) contain
high concentrations of ergosterol, also food spoiling Mucor plumbeus (Taniwaki et al.,
2009). In contrast, no ergosterol but high concentrations of cholesterol were measured
in chytridiomycetes (Weete et al., 1989; Kagami et al., 2007). Until now, no
information has been available on the ergosterol concentration of anaerobic fungal
species found in cattle, such as Anaeromyces, Orpinomyces, Caecomyces, or Piromyces
(Griffith et al., 2009).
The majority of microbial data on faeces samples are based on colony forming units
(CFU) or thallus forming units (TFU), counted on plates or as the most probable