The objective of this study was to evaluate the effect of buffering agent (NaHCO(3) and MgO) or substituting Dried Sugar Beet Pulp (DSBP) with barley on milk yield, composition of milk, some blood parameters and ruminal fermentation in cows. In the experiment, four lactating Holstein cows with similar age, lactation period and milk yield were utilized. Cows with second phase of lactation were selected. Treatments consisted of control (40% Barley), control+1% NaHCO(3) (NaHCO(3)), control+1% NaHCO(3)+0,5% MgO (MgO) and barley substituted with DSBP. All diets were calculated to be isocaloric and iso-nitogeneous. The experiment was a 4x4 Latin square design. While milk yield was significantly higher in animals fed diets containing NaHCO(3)+MgO compared with animals fed control, compositions of milk were not significantly different among the groups. Addition of NaHCO(3), NaHCO(3) + MgO significantly increased (p<0.05) acetic acid concentrations but did not affect blood parameters. In conclusion addition of NaHCO(3) or NaHCO(3) + MgO increased milk yield but did not affect composition of milk. An increase in ruminal acetic acid concentrations and acetic/propionic acid ratio due to buffering agent is an important finding. It must be revaluated the use of supplements in feeding diets since they decrease propionic acid level.