Microbial biomass in faeces of dairy cows affected by a nitrogen deficient diet

Abstract

Since more than half of the faecal nitrogen (N) originates from microbial N, the objective of the study was to develop a method for quantitatively detecting microbial biomass and portion of living microorganisms in dairy cattle faeces, including bacteria, fungi and archaea. Three techniques were tested: (1) the chloroform fumigation extraction (CFE) method, (2) detection of the fungal cell-membrane component ergosterol and (3) analysis of the cell wall components fungal glucosamine and bacterial muramic acid. In a second step, an N deficient (ND) and an N balanced (NB) diets were compared with respect to the impacts on faecal C and N fractions, microbial indices and digestibility. The mean values of microbial biomass C and N concentrations averaged around 37 and 4.9 mg g(-1) DM, respectively. Ergosterol, together with fungal glucosamine and bacterial muramic acid, revealed a 25% fungal C in relation to the total microbial C content in dairy cattle faeces. Changes in ruminal N supply showed significant effects on faecal composition. Faecal concentrations of NDF, hemicelluloses and undigested dietary N and the total C/N ratio were significantly higher in ND treatment compared to the NB treatment. N deficiency was reflected also by a higher microbial biomass C/N ratio. It was concluded that the assessment of microbial indices provides valuable information with respect to diet effects on faecal composition and the successive decomposition. Further studies should be conducted to explore the potentials for minimising nutrient losses from faeces.

Quantitative microbial indices in biogas and raw cattle slurries

“…Concentrations of the fungal cell‐membrane component ergosterol in the current biogas and raw slurries are similar to those in the feces of heifers and dairy cows reported by Jost et al. , who measured a range from 2.2 to 13.2 μg ergosterol g −1 DM. The concentrations of cell wall‐derived microbial C was also similar, but at the lower end of the concentrations obtained by Jost et al.…”

“…The concentrations of cell wall‐derived microbial C was also similar, but at the lower end of the concentrations obtained by Jost et al. , who measured a range from 21 to 50 mg microbial C g −1 DM. Consequently, the ratio of fungal GlcN to ergosterol is smaller in the current slurries than in cattle feces and only slightly above the chitin to ergosterol ratio of 40 obtained by Matcham et al.…”

“…Consequently, the coefficient of variation was markedly reduced compared with the data presented by Jost et al. .…”

“…These effects might be related to the size of the added microbial community as suggested by Jost et al. , who measured microbial biomass C and microbial biomass N, fungal ergosterol, bacterial muramic acid (MurN), and fungal glucosamine (GlcN) as quantitative indices for microorganisms in cattle feces. Classical, most probable number, and plate count techniques discriminate noncultivable microorganisms, contributing more than 80% to the total species number [].…”

“…In soil, the majority of amino sugars are accumulated as microbial residues in soil organic matter [26]. However, this was not the case in freshly and dynamically decaying feces, where the largest percentage of GlcN and MurN was still in the fungal and bacterial biomass [4,8,23]. For this reason, ergosterol and amino sugars were analyzed in biogas and raw slurries obtained from the six farms participating in the study of Wentzel et al [27], to investigate the following hypotheses: (i) Biogas slurries contain less ergosterol and amino sugars than raw slurries.…”