The effect of feeding essential oils on broiler performance and gut microbiota.

1. In this study the effect of a blend of essential oils (EO) comprising 15 g/tonne thymol and 5 g/tonne cinnamaldehyde on the performance and intestinal microbiota of broilers was investigated. 2. A total of 720 male Ross broilers were divided into two dietary treatments with 12 replicate pens per treatment. Broilers were given a control soybean-wheat-based diet with or without added EO in two diet phases (0-21 d and 22-42 d). 3. The blend of EO increased body weight gain of broilers from 0 to 42 d by 45%. 4. Caecal microbiota were affected by the EO blend; in particular increases in the proportions of Lactobacillus and Escherichia coli at 41 d was observed. 5. The EO blend had major effects on caecal metabolites. The proportion of caecal butyrate at 20 and 41 d of age increased, whereas the proportion of caecal acetic acid at 20 d, and propionic acid and isovaleric acid at 41 d, decreased with the EO blend. In addition, the caecal proportion of spermine increased and tyramine decreased at 41 d of age with the EO treatment. 6. The present study shows that EO supplementation exerts a positive effect on intestinal microbiota with a concomitant enhancement in growth performance. The study suggests that modulation of broiler gut microbiota composition and activity through the administration of EO offers an effective means for improving broiler performance.