Addition of fibrolytic and amylolytic enzymes in dairy cow diets aims to increase digestibility of NDF and starch, leading to better performance of the animals. The aim of this study was to evaluate the effect of exogenous fibrolytic (FIBROZYME, Alltech Inc., Nicholasville, KY) and amylolytic (AMAIZE Alltech Inc.) on performance and ruminal fermentation. Eight multiparous Holstein cows 133 ± 44.1 (mean ± SD) DIM, 532 ± 83.2 kg of BW and 31.8 ± 5.70 kg/d of milk blocked according to milk yield were used in a 4 × 4 Latin square experimental design. Treatments were as follows: 1) Control, basal diet without exogenous enzymes; 2) Fibrolytic enzyme, provision of 12 g/d (51 IU of xylanase activity/kg diet DM); 3) Amylolytic enzyme, provision of 8 g/d (203 FAU/kg diet DM); and 4) Both fibrolytic and amylolytic enzymes added at the same rate in individual treatments. Each 21-d experimental period included 14 d adaptation and 7 d sampling. Individual corn silage and orts samples were analyzed for DM, crude protein, ether extract, ash, NDF and starch. Milk yield was recorded and milk samples were analyzed for fat, lactose and crude protein. Ruminal liquid was collected (5 different sites within rumen) on 20th day of each experimental period, before the morning feeding (time 0), and after 2, 4, 6, 8, 10, 12, 14 and 16 h relative to the morning feeding, and was evaluated for pH, ammonium N and SCFA. Data were analyzed using the MIXED of SAS, means were adjusted by the LSMEANS procedure and interaction effect F_l × A_m were decomposed using Fisher’s protected LSD means test. Exogenous enzymes no effect (P ≥ 0.104) on intake or milk production (kg/d). Amylolytic enzyme decreased (P = 0.022) milk protein (kg/d) but had no effects (P ≥ 0.247) on lactose or fat production. Enzymes showed no effect (P ≥ 0.112; Table 3) on most ruminal characteristics. Amylolytic enzymes raised butyrate concentration in the absence of fibrolytic enzymes (interaction, P = 0.043). In summary, exogenous enzymes did not affect productive performance; however, amylolytic enzymes increased butyrate concentration, without other ruminal alterations.