The aim of the trial was to evaluate the performance and concentration of ketone bodies in the blood of early lactation cows supplemented with fibrolytic enzymes (750 mL/ T DM; Xylanase 350,000 BXU/g, Cellulase10,000ECU/g, AB Enzymes, Finland) in diets with different forage levels. Twenty Holstein × Zebu cows (46 ± 31 d in milk), blocked according to yield, DIM and parity, were individually fed for 132 d divided into 6 periods of 8 d adaptation and 14 d measurements in a 2 × 2 factorial randomized complete block design. The treatments consisted of 4 groups: (1) low forage (53.8%) without enzyme (LF); (2) low forage with enzyme (LFE); (3) high forage (62.3%) without enzyme (HF); (4) high forage with enzyme (HFE). The LF (33.07 kg/d) and LFE (31.72 kg/d) groups had higher milk yield than the HF group (27.01 kg/d), with the HFE group being intermediate (30.42 kg/d) (P = 0.02). 4% FCM (P = 0.022) and ECM (P = 0.044) showed the same behavior. There was a tendency for LF (1.27 kg/d) and LFE (1.23 kg/d) to present a higher fat yield than the HF group (1.08 kg/d), with the HFE group being intermediate (1.18 kg/d) (P = 0.068). LF had a tendency (P = 0.058) to present higher solids yield in relation to the HF and HFE groups. The LFE and LF groups had higher lactose content than the HF group, with the HFE group being intermediate (P = 0.001). Cows fed the LF diet had higher (P < 0.001) protein content (3.30 vs 3.14%) and higher (P = 0.001) lactose yield in relation to the cows that received the HF diet, regardless of enzyme addition. The protein yield of the LF group was similar to the LFE group and higher than the others (P = 0.005). The HFE group presented higher urea nitrogen content (P = 0.001) and tendency of higher blood ketone concentration (P = 0.059) compared with the others. To conclude, addition of enzyme improved the performance of cows fed diets containing a higher proportion of forage, approaching a similar level of performance as animals receiving a lower proportion of forage and higher proportion of concentrate.