The effects of different levels of fennel, savory essential oils and their mixtures on performance, immune system, antioxidant parameters and inter-leukin-6 gene expression in broilers

Objective Herbal essential oils are added to the poultry diet for a variety of reasons, such as improving performance, production and increasing the level of immunity. This study was conducted to investigate the effects of fennel and savory essential oils and their mixtures on growth performance, carcass characteristics, antioxidant parameters and hepatic interleukin-6 gene expression in broilers. Materials and methods The study was conducted in a completely randomized design with a 3 × 3 factorial arrangement with 9 treatments and 4 replications, each replication containing 15 birds. (540 Ross 308 broiler chickens). The experimental diets included the levels of 0 g/kg, 0.15 g/kg and 0.25 g/kg of fennel and savory essential oils and their mixture. Feed intake, weight gain and feed conversion ratio were calculated at starter (1-10 days), grower (11-24 days) and finisher (25-42 days). Each repeated three birds were bled at day 42. Interleukin-6 gene expression was performed on day 42. The ileum contents were sampled at 42 days of age to determine the microbial population.   Results The results showed that in the finisher (25-42), the experimental groups that received the essential oil had a lower conversion ratio than the control treatment. Among the experimental groups, the mixture of 0.25 fennel + 0.25 savory essential oils (g/kg feed) had the best production index (p<0.05). The essential oils used reduced the amount of malondialdehyde produced in the broiler drumstick (p<0.05). Herbal compounds increased the lactobacillus and reduced the coliforms and E. coli in the contents of the ileum. All savory supplementated groups except 0.25 (g/kg) + fennel 0.15 (g/kg) increased expression of hepatic interleukin-6 gene.   Conclusions Diets containing 0.25 (g/kg)fennel + 0.25 (g/kg) savory essential oils had the highest effect on improvment of the performance and expression of the broiler liver gene.