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The study was conducted with 40 clinically healthy (equal in both sexes) broiler chickens. Biosamples were taken at the end of the finishing period (day 41) in each group, from each bird, from all parts of the intestinal tract. Durable histological preparations were made by classical methods with each biosample. In the histological study, it was found that there was a microstructured change in all segments of the intestinal mucosa in the two experimental groups – first one, which received Ecodiar® liquid 5% to the drinking water, in dosage 0.5 ml of drug formulation/L water, and second one, which received Ecodiar® powder 5% to the feed, in dosage 0.5 g of drug formulation/kg of feed. In the third experimental group, which received 5 ml of 1% oregano oil/kg of feed and in the fourth (control) group, no histological changes in the intestinal wall were found. In the histometric study, the highest intestinal villi were found in the ileum, followed by the duodenum and the jejunum. Intestinal crypts had the largest outer diameter in the caecum, followed by the ileum, jejunum and duodenum. These two parameters showed different histometric values in each of the test groups of broiler chickens and each of the intestinal segments examined.