Lactobacillus buchneri is a heterofermentative bacteria recommended to be applied to forages more susceptible to spoilage and aerobic instability such as small grain or high moisture silages. It may affect rumen fermentation since the hetero-fermentation products (acetic acid, CO₂) are used by methanogenic microorganisms as substrates for the biomethane synthesis in the rumen. In consequences, these may lead to increase in gross energy losses from diet and aggravate negative influence of ruminant production on the environment. The aim of the study was to determine the effect of L. buchneri on rumen methanogenesis and fermentation profile of sorghum whole crop cereal and bagasse ensiled without additive (SWCC0, SB0) and with bacterial inoculant (SWCC1, SB1). During in vitro rumen fermentation gas production, methanogenesis and volatile fatty acids (VFA) profile of ruminal fluid were measured. The addition of L. buchneri decreased the acetate concentration after 8h of in vitro rumen fermentation SWCC and SB silages. The material affects the acetate, propionate, butyrate, isovalerate and valerate concentration after 8h of in vitro rumen fermentation. Moreover, material affects the propionate, isobutyrate and butyrate concentration after 24h of fermentation. L. buchneri increased the level of methane after 8h fermentation of SWCC and SB. However, after 24h of fermentation L. buchneri decreased the concentration of methane in SWCC silage. The fermentation profile (24h) of SB silages was characterized by higher levels of methane compared to SWCC silages.