A semi-field study was carried out to evaluate the effect of two medicinal herbs, individually and in combination, on growth performance, carcass traits, nutrient digestibility and immune response of broiler chickens. A total of 384 one-day-old straight-run Arbor Acres broiler chickens were allocated into 24 floor pens prepared in a commercial broiler house. Pen-groups were fed one of the following five diets for 42 days: a basal corn-soybean meal diet as control (5 pens), the same basal diet plus 200 ppm virginiamycin (V; 4 pens), the same basal diet supplemented with 0.4% peppermint (Mentha piperita) leaves (P; 5 pens), 0.4% tarragon (Artemisia dracunculus) leaves (T; 5 pens) or with 0.2% tarragon leaves + 0.2% peppermint leaves (P+T; 5 pens). The results showed that performance traits, including average body weight, body weight gain, feed intake and feed conversion ratio were not affected by dietary treatments (P>0.05). No significant differences were detected between the control and experimental groups in apparent digestibility of nutrients and antibody titer against newcastle disease virus (NDV). Slaughter traits of herb or antibiotic supplemented groups did not differ significantly from those of the non supplemented control group. In conclusion, the additives tested had no impact on broiler growth and health status. پرونده مقاله