Using 24 hours in vitro cultures of rumen microorganisms, this study investigates the effect of buffering capacity of 2 inorganic compounds (M1=119.43 and M2=116.50 meq/L) on the in vitro rumen acidogenic value (AV), medium pH, dry matter disappearance (INVDMD) and methane emission of lactating dairy cow diets containing various forage to concentrate ratios as 40:60 (FC40:60) and 30:70 (FC30:70) in a completely randomized design. Inorganic compounds were included in the experimental diets at the rate of 0.0, 10 or 20 g/kg DM. Diet with higher amount of concentrate caused a decline in medium pH, an increase in both AV and IVDMD. The acidogenic value of FC40:6 containing M2 at 20, M1 at 10 and 20 g/kg DM and FC 30:70 plus M1 and M2 at 20 g/kg DM was the lowest. The lowest level of CH 0 4 emission (mL/0.20 g DM) was observed in FC30:70 plus M1 at the rate of 10 g/kg DM, while the highest level belongs to FC40:60 plus M1 at 10 g/kg DM and FC30:70 containing M1 at 20 and M2 at 10 g/kg DM. It has been concluded that the higher buffering capacity of a lactating diet might reduce the rumen acid load and increased IVDMD, while a diet with higher amount of concentrate causes to decline rumen methane emission.

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