Our objective was to determine the effects of replacing alfalfa silage (AS) NDF with corn silage (CS) NDF at 2 levels of forage NDF (FNDF) on performances and efficiencies of Holstein (H) and Jersey (J) cows. Twelve H and 12 J cows (primiparous and mid-lactation) housed in tie-stalls, fed once and milked twice daily, were fed 4 total mixed rations in a 2 × 2 factorial arrangement of FNDF level (20 and 26% of DM) and FNDF sources (70:30 and 30:70 ratio of AS:CS NDF). All diets had identical crude protein (16.5% of DM) and starch (24% of DM). The design was a split plot triplicated 4 × 4 Latin square with breed in the main plot and diet in subplots. Data presented here were collected in wk 3 and 4 of each 28-d period. Data were analyzed using proc Mixed of SAS. Effects presented here had P < 0.05. Holstein cows had greater dry matter intake (DMI, 22.5 vs. 16.8 kg/d), milk yield (MY, 33.2 vs. 21.3 kg/d), fat protein corrected milk (FPCM, 32.7 vs. 24.9 kg/d), fat yield (FY,1.37 vs. 1.12 kg/d), protein yield (PY, 0.97 vs. 0.76 kg/d), and lactose yield (LY, 1.61 vs. 1.01 kg/d) but lower fat (4.13 vs. 5.28%) and protein (2.93 vs. 3.56%) than J cows. Cows fed low FNDF diet had greater DMI (20.5 vs. 18.8 kg/d), MY (27.7 vs. 26.7 kg/d), FPCM (29.5 vs. 28.2 kg/d), FY (1.27 vs. 1.22 kg/d), PY (0.89 vs. 0.83 kg/d), LY (1.35 vs. 1.27 kg/d), protein (3.28 vs. 3.20%) and lactose (4.83 vs. 4.77%) but lower feed efficiency (FE, 1.35 vs. 1.43 kg MY/kg DMI; 1.45 vs. 1.52 kg FPCM/kg DMI), net energy of lactation (NEL) efficiency (0.71 vs. 0.74 Mcal milk NEL/NEL intake) and N efficiency (0.26 vs. 0.27 milk N/N intake) than cows fed high FNDF diet. Cows fed AS based diet had lower DMI (19.1 vs. 20.3 kg/d), MY (26.9 vs. 27.6 kg/d), FPCM (28.3 vs. 29.3 kg/d), FY (1.22 vs. 1.26 kg/d), PY (0.84 vs. 0.88 kg/d), LY (1.29 vs. 1.33 kg/d) and protein (3.22 vs. 3.27%) but greater FE (1.42 vs. 1.36 kg MY/kg DMI) than cows fed CS diet. In conclusion, cows fed high FNDF and high AS based-diets were more efficient than their counterpart, but breed did not affect efficiencies.