Abstract: The purpose of this experiment was to study the effect of different levels of thyme essential oil on growth performance,serum protein and cytokines of Mahua broilers.768 one-day-old broilers were randomly allocated into 8 groups with 4 replicates in each group and each replicate contained 24 broilers. The control group was fed with basic diet,Ⅰ to Ⅶ groups were fed the basal diet supplemented with 0.05,0.10,0.15,0.20,0.25,0.30 and 0.35 mg/kg thyme essential oil,respectively.The whole experiment period was 42 days,including two phases of days 1 to 21 (starter period) and days 22 to 42 (finisher period).The results showed that there were no significant differences in all the indices about growth performance during the starter period among all groups (P>0.05). Compared with the control group,the ADG during the finisher period in the Ⅱ to Ⅵ groups was extremely significantly increased (P<0.01),the F/G during the finisher period in the Ⅲ,Ⅳ,Ⅵ groups was significantly decreased (P<0.05).Compared with the control group,the serum content of ALB on day 42 in the Ⅱ group was significantly decreased (P<0.05),the serum content of GLB on day 21 in the Ⅱ to Ⅴ,Ⅶ groups was significantly increased (P<0.05),the serum content of A/G during the whole period in the Ⅱ,Ⅳ,Ⅴ groups was significantly decreased (P<0.05).Compared with the control group,the serum content of IL-1 on day 42 in the Ⅶ group was significantly increased (P<0.05),but there were no significant differences in the contents of IL-4,TNF-α and IFN-γ during the whole period among all groups (P>0.05).In conclusion,thyme essential oil could promote the internal protein deposition,improve the growth performance and enhance the immune regulation of Mahua broilers,the suitable level was 0.10 to 0.25 mg/kg.

Key words: thyme essential oil; growth performance; serum protein; cytokine