An experiment was conducted to evaluate the synergistic efficacy of formic acid and Origanum vulgare in broiler diets. Experiments were carried out as a completely randomized design in a factorial arrangement (3×3) with 4 replicates of 10 chicks in each pen. Factors included 3 concentrations of formic acid (0, 1% and 2%) and 3 concentrations of Origanum vulgare powder (0, 1% and 2%). BW and cumulative feed intake were measure weekly. Blood characteristics, relative weight and length of different parts of the carcass, gastrointestinal pH, villi length, and crypt depth were measured at 42 d of age. Addition of 2% formic acid significantly increased BW gain at first week and also during the 14 and 21 d of age but had no obvious effect on the BW gain after 21 d of age. Formic acid supplementation did decrease FCR without any consequence in feed intake during the experimental period (P 0.05). The inclusion of Origanum vulgare had no significant effect on BW, feed intake and FCR during the experimental period. The inclusion of Origanum vulgare linearly decreased pH of gizzard, duodenum, jejunum, ileum but increased pH of caeca content (P 0.01). Addition of 2% formic acid significantly decreased pH of gizzard, duodenum, jejunum, ileum but increased pH of caeca content (P 0.01). The synergistic effect of formic acid and Origanum vulgare on pH of different part of the gastrointestinal content of broiler was obvious. There was no significant interaction of formic acid and Origanum vulgare on performance characteristics of broiler fed both of this products. Results of current study showed that using mix of the organic acid and phytogenic product could make a healthy intestine in broiler chicks.
