In experiment 1, we evaluated the combined effects of two grain (barley vs. corn) and forage sources (corn silage vs. alfalfa hay) on ruminal fermentation, nutrient digestibility, performance, and blood metabolites of dairy cows and it has been showed that cows fed corn grain (CG) consumed more DM and produced more actual and energy-corrected milk than those fed barley grain (BG). Total tract starch (952 vs. 987 g/kg) and CP (687 vs . 743 g/kg) digestibility were lower for cows fed CG than those fed BG. The ruminal propionate concentration tended to be lower for cows fed CG than those fed BG, indicating a difference in ruminal fermentability of these two cereal grain sources. Energy-corrected milk yield (42.6 vs. 40.7 kg/d) and milk fat concentration (30.6 vs. 29.2 g/kg) tended to be greater for cows fed diets with alfalfa fay (AH) than those fed diets with corn silage (CS). Moreover, cows fed AH had higher ruminal acetate to propionate ratio despite having similar total volatile fatty acids production and nutrient digestibility compared to CS-fed cows. However, cows fed CS spent more time ruminating and had greater total chewing activity compared to cows fed AH. In conclusion, replacement of BG with CG improved performance by enhancing nutrient intake; however, the expected positive effects of replacing CS with AH in barley-based diets may be masked by interference of differences in forage PS. In experiment 2 we investigated the effects of substituting beet pulp (BP) for different grains (barley or corn) in the diet of high producing dairy cows on intake, feeding behavior, nutrient digestibility, ruminal fermentation, milk production, and feed conversion efficiency. Results of this study shows that Cows fed CG consumed more DM and produced more actual and energy-corrected milk than those fed BG. Total tract starch (952 vs. 987 g/kg) and CP (687 vs . 743 g/kg) digestibility were lower for cows fed CG than those fed BG. The ruminal propionate concentration tended to be lower for cows fed CG than those fed BG, indicating a difference in ruminal fermentability of these two cereal grain sources. Energy-corrected milk yield (42.6 vs. 40.7 kg/d) and milk fat concentration (30.6 vs. 29.2 g/kg) tended to be greater for cows fed diets with AH than those fed diets with CS. Moreover, cows fed AH had higher ruminal acetate to propionate ratio despite having similar total volatile fatty acids production and nutrient digestibility compared to CS-fed cows. However, cows fed CS spent more time ruminating and had greater total chewing activity compared to cows fed AH. In conclusion, replacement of BG with CG improved performance by enhancing nutrient intake; however, the expected positive effects of replacing CS with AH in barley-based diets may be masked by interference of differences in forage PS. Key Words: Alfala hay, Beet pulp, Corn silage