Methanogenic Population and CH4Production in Swedish Dairy Cows Fed Different Levels of Forage
ABSTRACTMethanogenic community structure, methane production (CH4), and volatile fatty acid (VFA) profiles were investigated in Swedish dairy cows fed a diet with a forage/concentrate ratio of 500/500 or 900/100 g/kg of dry matter (DM) of total DM intake (DMI). The rumen methanogenic population was evaluated using terminal restriction fragment length polymorphism (T-RFLP) analysis, 16S rRNA gene libraries, and quantitative real-time PCR (qRT-PCR). Mean CH4yields did not differ (P> 0.05) between diets, being 16.9 and 20.2 g/kg DMI for the 500/500 and 900/100 diets, respectively. The T-RFLP analysis revealed that populations differed between individual cows and that each individual population responded differently to the diets. The 16S rRNA gene libraries revealed thatMethanobrevibacterspp. dominated for both diets. CH4production was positively correlated with a dominance of sequences representing T-RFs related toMethanobrevibacter thaueri,Methanobrevibacter millerae, andMethanobrevibacter smithiirelative toMethanobrevibacter ruminantiumandMethanobrevibacter olleyae. Total numbers of methanogens and total numbers ofMethanobacterialeswere significantly higher with the 500/500 diet (P< 0.0004 andP< 0.002, respectively). However, no relationship was found between CH4production and total number of methanogens. No differences were seen in total VFA, propionic acid, or acetic acid contents, but the molar proportion of butyric acid in the rumen was higher for the 500/500 diet than for the 900/100 diet (P< 0.05). Interestingly, the results also revealed that a division of the identified methanogenic species into two groups, suggested in the work of King et al. (E. E. King, R. P. Smith, B. St-Pierre, and A. D. G. Wright, Appl. Environ. Microbiol.77:5682–5687, 2011), increased the understanding of the variation in CH4production between different cows.