Fütterungsbedingte mikrobielle Zusammensetzung von Rinderkot ...

5. Microbial biomass in faeces of dairy cows affected by a nitrogen deficient diet 37
a high C/N ratio is expected to have long-term beneficial effects on soil biological
functioning and nutrient use efficiency of plants (Haynes and Naidu, 1998; Mäder et al.,
2002). For plant uptake, faecal N has to be mineralised after manure application.
Mineralisation of faecal N is influenced, among other things, by variation in the fibre
fractions (NDF, ADF, and ADL) and by the C/N ratio (Kyvsgaard et al., 2000). The
organic bound N fraction is mineralised more rapidly in the soil than the fibre bound N
(Sørensen et al., 2003; Powell et al., 2006).
Differences in the concentration of nutrients and organic components in the diet
also affect the microbial community of the faeces (Van Vliet et al., 2007). As more than
half of the faecal nitrogen originates from microbial N (Larsen et al., 2001), knowledge
of the microbial biomass content in faeces is important to assess the efficiency of
nutrient use. However, methods for quantifying microbial biomass and living
microorganisms in fresh faeces are rare. With the exception of pathogens and coliform
bacteria shed in faeces (Van Kessel et al., 2007), microbial populations of the intestinal
tract and their relationship to host diet remain less well characterized (Frostegård et al.,
1997; Gattinger et al., 2007; Van Vliet et al., 2007). The intestinal tract of cattle is
colonized by a highly dynamic community of bacteria, archaea and fungi. Methods that
enable the assessment of the total microbial biomass in faeces provide valuable
information on the dynamics of fermentation processes and microbiological populations
within the large intestine and after defecation.
In general, plate count approaches discriminate archaea and other non-cultivable
microorganisms, which contribute more than 80% to the total number of species
(Ouwerkerk and Klieve, 2001). Direct microscopic approaches often severely
underestimate fungi (Joergensen and Wichern, 2008). New molecular techniques have
made it possible to quantify certain microbial species or genera in different substrates
and also in intestinal contents of cattle (Frey et al., 2010). The extraction of DNA
followed by analysis of its composition provides important information on the microbial
community composition of faeces (Van Vliet et al., 2007; Sekhavati et al., 2009), but
usually reveals no information on the biomass, due to losses during extraction and
unknown or highly variable DNA concentrations within different microorganisms
(Leckie et al., 2004; Joergensen and Emmerling, 2006).
In contrast to the methods listed above, the chloroform fumigation extraction (CFE)
method is able to estimate the biomass of all microorganisms surrounded by an intact
cell-membrane, i.e. bacteria, fungi, and archaea. Additionally, the method has proven to