There is a lack of research on potential effects of supplementation on metabolic profile in grazing dairy cows. Therefore, 45 Holstein dairy cows (147 DIM, 544 kg BW) were assigned to a 3 × 3 Latin square design replicated 15 times to evaluate the effect of sensory additive compound by natural plant extracts with a sweet flavor (ProEfficient, PE) on leucocyte and metabolic profile of grazing dairy cows supplemented with concentrate. Cows were blocked by parity in 15 blocks and within blocks randomly assigned to 3 treatments: 0 kg/d concentrate (0C); 5 kg/d control concentrate (CC); and 5 kg/d CC with 30 g/d of PE (PEC). Cows grazed a kikuyu (Pennisetum clandestinum) pasture for 84 d in 3 28-d periods at a pasture allowance of 35 kg DM/cow. Pasture averaged 24.2% CP, 55.5% NDF, and 60.3% in vitro DM digestibility (IVDMD). Concentrates (44.3% corn, 11.2% wheat bran, 10.0% corn gluten feed, 8.6% rice meal, 8.4% soybean meal, 8.0% of sunflower meal, 9.5% mineral premix) were fed twice daily at milking and averaged 18.4% CP, 17.8% NDF, and 85.5% IVDMD. Blood samples were collected at 0900 h (3 h after supplementation) from the tail vein on d 3 of each period. One BD Vacutainer blood-collection tube and one plasma BD Vacutainer K₂EDTA were analyzed for hematological parameters, white blood cells (WBC), differential WBC count, fibrinogen concentration, and parameters of blood biochemistry at the Animal Diagnosis Laboratory of Universidad de Antioquia. Data were analyzed using a mixed model that included the fixed effects of treatment, block, period, their 2-way interactions, and the random effect of cow within block. Supplementation with PEC (P = 0.07) improved the total count of leucocytes compared with 0C (8.10 vs. 7.62 cells × 10³ µL, SEM 0.37). Concentrate supplementation increased (P = 0.03) granulocytes count (3.31 vs. 2.85 cells × 10³ µL, SEM 0.17). Lymphocytes percentage was lower (P = 0.10) with PEC than with 0C (57.8 vs. 61.3%, SEM 1.55). Total plasmatic proteins increased (P < 0.05) with PEC vs 0C (8.14 vs 7.98 g/L, SEM 0.08). The cells and components of immune system (leucocytes and total plasma proteins) tended to improve by adding PE to the concentrate supplemented to grazing dairy cows.