Our objective in this study was to evaluate the effects of feeding increasing exogenous carbohydrases levels on dry matter intake, milk yield and composition, and production efficiency of lactating dairy cows. Eight rumen cannulated Holstein cows [27.8 ± 5.3 (mean ± SD) kg of milk yield per day, 182 ± 58.6 d in milk, 590 ± 85.9 kg of body weight, 2.78 ± 0.160 of body condition score] were blocked by parity and milk yield, divided in 2 replicated Latin squares 4 × 4 and randomly assigned to the following treatments: 1) Control, basal diet with no enzyme; 2) Carb 1 (carbohydrases): diet with 10 g of a blend of 2 enzymes (xylanase, Ronozyme WX; β-glucanase, Ronozyme VP, DSM Nutritional Products, Basel, Switzerland); 3) Carb 2: diet with 20 g inclusion of a blend of 2 enzymes (xylanase, Ronozyme WX; β-glucanase, Ronozyme VP); 4) Carb 3: diet with 30 g inclusion of a blend of 2 enzymes (xylanase, Ronozyme WX; β-glucanase, Ronozyme VP). Experimental diets were formulated according to NRC (2001), with a 50:50 roughage to concentrate ratio and corn silage as unique roughage source. Each experimental period included 14 adaptation days and 7 sampling days. Individual dry matter intake and milk production were recorded daily; milk samples were collected for 3 consecutive days, during the morning and afternoon milking. Data were analyzed using the MIXED procedure of SAS Inst (2001), using linear and quadratic contrasts to evaluate dose response of enzyme inclusion and control vs. enzyme contrast. Carbohydrase inclusion increased (P = 0.027) milk fat yield (1.00 vs. 1.06 kg/d), while tended to increase (P ≤ 0.071) 3.5% fat-corrected milk yield (28.1 vs. 29.3 kg/d) and milk fat percentage (3.70 vs. 3.86) in contrast to control. Furthermore, carbohydrase tended to linearly increased (P ≤ 0.089) 3.5% fat and energy-corrected milk production efficiency. There were no effects on feed intake, milk yield, milk protein and lactose content, and milk production efficiency. Therefore, exogenous carbohydrase inclusion increases milk fat yield and brings benefits to dairy cows performance.