Abstract: 【Objective】 This experiment was conducted to investigate the effects of different levels of Bacillus licheniformis BCG on growth performance and health of broilers, explore the probiotic effect of BCG on broilers and provide theoretical basis for the application in production.【Method】 A single factor experimental design was adopted, 180 1-day-old Arbor Acres broilers with similar body weight (42.62 g±0.82 g) and good health conditions were selected and randomly divided into 3 treatments, and each treatment included 6 replicates with 10 chickens per replicate.The broilers in control group (CT group) were fed with the basal diet, and the broilers in Bacillus licheniformis treatment groups (BCG1 and BCG2 groups) were supplemented with 1.0×10⁸ and 1.0×10⁹ CFU/kg of Bacillus licheniformis BCG in the basal diet, respectively.The trial period was divided into two feeding stages, 1 to 21 days and 22 to 42 days, with a duration of 42 days.On days 21 and 42, the broilers in each group were weighed on an empty stomach in the unit of replication and feed intake at each stage was recorded to calculate average daily gain (ADG) and average daily feed intake (ADFI).Two chickens per replication were selected to collect blood and to measure blood routine indexes, serum biochemistry and serum immunity related indexes.On day 42, small intestine was separated after slaughtering, and the intestinal morphological structure was observed to measure villus height (VH), crypt depth (CD) and to calculate the ratio of villus height to crypt depth (VH/CD).【Result】 ① Compared with CT group, the body weight of broilers in BCG2 group was significantly increased on day 42 (P<0.05).During days 22 to 42, the ADG and ADFI in BCG2 group were significantly increased (P<0.05), and the former was significantly higher then that in BCG1 group (P<0.05).During days 1 to 42, both ADG and ADFI in BCG1 and BCG2 groups were significantly increased (P<0.05), and there was no significant difference between the BCG1 and BCG2 groups (P>0.05).② On day 21, compared with CT group, the contents of the serum immunoglobulin A (IgA), IgM and IgG in BCG2 group were significantly increased (P<0.05), and the endotoxin activity was significantly decreased (P<0.05).The content of serum IgA and IgM in the BCG 2 group were significantly higher than those in BCG1 group (P<0.05).On day 42, the addition of Bacillus licheniformis BCG had no significant effect on blood routine indexes and IgA, IgM and IgG contents (P>0.05).③ On day 42, the VH of jejunum in BCG2 group was significantly higher than that in CT group (P<0.05), and VH/CD of jejunum in BCG2 group was significantly higher than that in CT and BCG1 groups (P<0.05).【Conclusion】 Bacillus licheniformis BCG supplementation could improve the growth performance of broilers, enhance humoral immunity and intestinal barrier function in the early stage of broilers, and improve the morphological structure of the small intestinal tract.The prebiotic effect was better with the addition amount of 1.0×10⁹ CFU/kg.

Key words: Bacillus licheniformis BCG; broilers; growth performance; serum biochemical indexes; intestinal morphology