In this study, bacteria and methanogens involved in the decomposition of dairy cattle manure have been characterized via cultivation on selective microbiological media by the viable plate count technique. In addition, DNA was extracted from digested samples, and the 16S rRNA gene was amplified using six primer sets specific to bacterial and archaeal domain via PCR. The sequences of the PCR products were determined and compared to similar sequences in the GenBank database using the BLASTN tools to identify the closest relatives. By culture, E. coli, Salmonella, Shigella, and Campylobacter species were identified and belonged to the phylum Proteobacteria. Following, 16S rRNA analysis, Firmicutes (80%) was the most dominant bacterial phylum represented by the predominant order Clostridiales and genus Clostridium. Other members belonged to the phyla Proteobacteria and Spirochaetes. The phylum Euryarchaeota (100%) was the only observed archaeal domain with members that belonged to the dominant class Methanomicrobia and genus Methanocorpusculum. Other members were related to the order Methanobacteriales and Methanosarcinales. Results suggested that Clostridium sp, Clostridium related organisms, and other acidogens were responsible for the deconstruction of biomass-generating substrates metabolized by Methanocorpusculum and Methanobrevibacter species to produce methane via the fundamental hydrogenotrophic pathway.