This study aimed to analyze ruminal fermentation, methane emissions, and methanogen levels for different forage feed type and concentrate feed ratios. Alfalfa hay, oat hay, and a feed concentrate were used for in vitro fermentation experiments, at ratios of 9:1, 5:5, and 1:9 (forage:concentrate). After 24 h of incubation, rumen fermentation and methanogen level changes were evaluated. In the low forage treatments, the total gas, CH4, NH3-N, true dry matter digestibility, and total volatile fatty acid were higher than the other treatments, which were used as the parameters on which to assess rumen fermentation (P < 0.05). The feed ratio influenced the copy number for the total archaea and the genus Methanobrevibacter (P = 0.015, P = 0.010). The copy number result trend was like that for CH4 per digested dry matter (DDM). The PCR results and methanogen copy number analysis indicated that the composition of the methanogens affected the CH4 levels, not their copy number. The results of this study can be applied to predict rumen fermentation and methane emission patterns for cattle fed a variety of feedstuffs.