Lactating cow diets are comprised mostly of carbohydrates, which are not fully fermented by rumen microbes, limiting energy release from feed. The aim of this study was to evaluate exogenous fibrolytic (FIBROZYME Alltech Inc., Nicholasville, KY) and amylolytic (AMAIZEAlltech Inc.) enzymes in mid-lactation dairy cows. Thirty-two multiparous Holstein cows 181.3 ± 35.3 DIM, 571 ± 72.7 kg BW and 29.6 ± 5.24 kg/d of milk yield, blocked according to milk yield were randomly allocated to treatments in a 4 × 4 Latin square design. Treatments were (1) Control (CON), basal diet without exogenous enzymes; (2) Fibrolytic enzyme (FIB), provision of 12 g/d (51 IU of xylanase activity/kg diet DM); (3) Amylolytic enzyme (AMY), provision 8 g/d (203 FAU/kg diet DM); and (4) Both fibrolytic and amylolytic enzymes (FIB+AMY), enzymes added at the same rate as in individual treatments. Each 21-d experimental period included 14 d of adaptation and 7 d of sampling. Individual TMR and orts samples were collected and assessed for particle size distribution. From 17 to 19-d of each period feces were collected every 9 h to determine total-tract digestibility. Feeds, orts, and feces were analyzed for DM, crude protein, ether extract, ash, NDF, and starch. Indigestible NDF was used as internal marker to estimate daily fecal DM excretion. Milk yield was recorded and samples analyzed for fat, lactose, and crude protein. Data were analyzed using the MIXED procedure of SAS (version 9.3; SAS Institute Inc., Cary, NC). Enzymes addition had no effect (P ≥ 0.111) on intake. Cows fed amylolytic enzymes selected against large feed particles (>19 mm; P = 0.031), and slightly in favor of smaller particles (8 to 19 mm) only in the absence of fibrolytic enzymes (interaction; P = 0.024). Enzyme addition showed no effect on digestibility, milk yield, fat-corrected milk, or milk fat concentration. Either enzyme product alone reduced daily milk lactose and protein production (interaction, P ≤ 0.053). In summary, addition of exogenous enzymes had no effect on performance, intake, or digestibility but modified selection of feed particle sizes, lactose and protein production.