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A comparative study for broiler chickens using different drug formulations, containing oregano essential oil was added daily: Ecodiar® liquid 5% to the drinking water; Ecodiar® powder 5% and oregano oil 1% to the complete feed from the 1 to the last day of the finishing period (day 41). The experiment included 80 clinically healthy broiler chickens of the both sexes, 1-day old, hybrid Cobb-500, bred to the last day of the starter (n = 40) and bred to the last day of the finishing period (n = 40). In the dynamics (during the starter and finishing period), the indicators were determined: body weight, average daily gain, feed intake per capita/per day, energy and protein intake, feed efficiency, energy efficiency and crude protein efficiency per 1 kg gain, weight of the carcass, liver, heart, gizzard, spleen and bursa of Fabricius. The our results showed that in body weight gain and carcass, liver, spleen and heart weights of the broilers without statistically significant differences were observed compared to the control group during the starter and the finishing periods. In the gizzard weight of broilers that received Ecodiar® liquid 5% and Ecodiar® powder 5% with statistically significant differences were observed during the starter period, compared to the control group (p < 0.05). In weights of the bursa Fabricius in broilers that received Ecodiar® liquid 5% and 1% of oregano oil (p < 0.05) with statistically significant difference was observed during the grower‐finisher period