The majority of Brazilian dairy farms use pull-type, one row forage harvesters for ensiling corn. For such machines, a kernel processor (KP) was developed (MU9000462–0 U2 INPI patent). We evaluated the response of cows to corn silage (CS) short particles-no KP (S, 3 mm theoretical cut) compared with long particles-KP (L, 8.5 mm). The supplementation of fibrolytic enzyme (F, Fibrozyme, Alltech) was evaluated in a 2 × 2 factorial. Sixteen individually fed Holsteins (110 ± 62 DIM) received treatments in 28-d periods, 4 × 4 LS. Corn was harvested at half milk line maturity and ensiled in 3 m diameter bag silos for 138 d. Silage S had 44.8% of particles below the 8 mm screen and L had 25.3%. Diets contained 31.6% of DM as the treatment CS, 17.1% of a standard CS, 1.9% Tifton hay, and 31.7% starch. Diet S had 1.9% of DM as NDF above the 19 mm screen, 12.3% from 8 to 19 mm, and 17.8% below 8 mm, and L had 3.0%, 15.6%, and 13.9%, respectively. The TMR was mixed manually twice per day immediately before feeding to avoid particle size reduction. Silage L increased 4% FCM (29.5 vs. 28.2 kg/d, P = 0.09) and fat yield (P = 0.04), and had no impact on DMI (22.0 kg/d, P = 0.50). There were trends for reduced milk fat content and yield in response to F (P < 0.15). Silage S reduced ruminal fluid pH and the proportion of acetate in VFA, but increased butyrate and protozoa content (P < 0.05). Total-tract OM and NDF digestibility tended to be increased by F only when S reduced nutrient digestibility (P = 0.09 for interaction of CS and F).The daily urinary allantoin secretion was increased only when F supplemented S (P = 0.03 for interaction of CS and F). Fecal viscosity and DM content were also reduced when F was added to S (P < 0.02 for interaction of CS and F). The loss of visible damaged corn kernels in feces was reduced by F (P = 0.05), but the excretion of intact kernels was similar (P = 0.92). Silage L tended to increase rumination bouts/bolus (P = 0.10) and the duration of the first daily meal (P = 0.08), and increased chewing activity per day and per unit of DMI (P < 0.03). There was a trend for reduced PUN on F (P = 0.07). Fibrolytic enzyme was beneficial to digestion only when fiber digestibility was reduced by short particles CS. Long particles CS increased lactation performance and chewing activity.