Secondary plant compounds can modify rumen fermentation, cutaneous blood flow, sweat secretion, diet digestibility, and feeding behavior of dairy cows. Twenty-eight, individually fed Holsteins (181 ± 102 DIM) received a standard diet for 2 wk and 2 dietary treatments for 8 wk, in a covariate adjusted randomized block design. Treatments were: Control (CTL) or a microencapsulated blend of essential oils and pepper extract (BEO. Carvacrol, cinamaldehyde, eugenol, and capsaicin. Activo Premium. 150 mg/kg DM). BEO decreased DMI (20.1 vs. 19.5 kg/d; P = 0.05) and increased milk yield (30.1 vs. 30.8 kg; P = 0.04), improving the milk to feed ratio (1.53 vs. 1.63; P < 0.01). Milk fat content tended to increase with BEO (P = 0.10), but protein, lactose, total solids, MUN, and SCC did not differ (P > 0.21). BCS and BW were similar (P > 0.39). BEO reduced ruminal acetate (57.8 vs. 51.4% of VFA; P = 0.01) and increased propionate (26.1 vs. 31.3% of VFA; P = 0.02), decreasing the A/P ratio (2.3 vs. 1.7; P = 0.03). Total-tract digestibility of DM, OM, and NDF were similar (P > 0.20), but there were trends for increased non-NDF OM digestibility (P = 0.07) and digestible OM intake (P = 0.06) on BEO. Cows on BEO ingested a greater proportion of the daily feed intake from 6AM to 12PM (P = 0.02) and tended to have longer duration of the first meal (P = 0.08), whereas CTL cows tended to ingest more from 7PM to 6AM (P = 0.06). BEO induced selective sorting in favor of small feed particles (P < 0.01) and refusal of large particles (P < 0.03) in the morning. Ingestion and rumination times were similar (P > 0.19). Viscosity of manure was reduced by BEO (P = 0.04). Treatments had no effect on PUN along the day, plasma glucose content, and the urinary secretion of allantoin (P > 0.42). BEO increased the concentration of O₂ in jugular blood (P < 0.01), but had no effect on pH, pCO₂, HCO₃^-, total CO₂, and base excess (P > 0.46). Sweating rate at d 14 was increased by BEO (P = 0.05). No difference was detected in rectal and skin temperatures and in respiratory frequency (P > 0.21). The supplementation of dairy cows with BEO affected feeding behavior, reduced the A/P ratio in rumen fluid, and improved feed efficiency.