Abstract: 【Objective】 This experiment was conducted to investigate the effect of glycyrrhizic acid(GA) on the immune function of Yellow-feathered broilers.【Method】 A total of 300 one-day-old healthy Yellow-feathered broiler chickens with similar body weight were selected and randomly divided into 6 groups, with 5 replicates in each group, 10 in each replicate, namely the normal saline group (NS), lipopolysaccharide (LPS) group, astragalus polysaccharide group(APS), high-dose glycyrrhizic acid group(GA_H), middle-dose glycyrrhizic acid group(GA_M) and low-dose glycyrrhizic acid group(GA_L).The NS group was intraperitoneally injected with 2 mL of 0.9% sterile saline in the morning of 14, 16, 18 and 20 days old, and the other groups were injected with an equal volume of LPS solution (1.5 mg/kg BW) at the same time to establish immune stress model in vivo. NS group and LPS group were fed with the basal diet, while APS group, GA_H, GA_M and GA_L experimental groups were supplemented with 400 mg/kg astragalus polysaccharides (APS) and 120, 100, 80 mg/kg of GA on the basis of the basal diet at the stage of establishment of the stress model and 3 days before and after the stage (11-23 days).The experimental period was 49 days.At 21, 28, 35, 42 and 49 days of age, 2 chickens were randomly selected in each replicate to collect wing vein blood, and the contents of CD4, CD8 and immunological active material IgA, IgG and IgM in serum were determined by enzyme-linked immunosorbent assay (ELISA).【Result】 Compared with NS group, at the age of 21-49 days, the serum CD4 molecule content of the other 5 groups of broilers was extremely significantly decreased (P<0.01), while the serum CD8 molecule, IgA, IgG, IgM (except GA_H group and APS group) were increased.Compared with LPS group, the serum CD4 molecular contents of broilers in APS group and three GA groups were increased, while the serum CD8 molecular contents were extremely significantly or significantly decreased (P<0.01;P<0.05).The serum IgA, IgG and IgM contents were extremely significantly decreased (P<0.01).In addition, among the three GA groups, the serum CD4 content of broilers was increased with the increase of GA supplementation, and the increase in the GA_H group was the closest to that in the APS group, especially at 42 days of age, there was no significant difference between GA_H group and APS group (P>0.05), and all were extremely significantly or significantly higher than those in the LPS group (P<0.01;P<0.05)。However, the serum CD8, IgA, IgG, and IgM contents of broilers showed a decreasing trend with the increase of GA supplementation, and the decrease in GA_H group was the closest to that in APS group.There was no significant difference in CD8 molecular content between the two groups (P>0.05), and at 35 and 49 days of age, there was no significant difference in CD8 molecular content between GA_H group and NS group (P>0.05).In terms of IgA content, there was no significant difference between GA_H group and APS group except at 35 days of age (P>0.05), and at 21 and 49 days of age, there was no significant difference between GA_H group and NS group (P>0.05).In terms of IgG content, there was no significant difference between GA_H group and APS group except at the age of 28 days (P>0.05), and at the age of 35 days, there was no significant difference between GA_H group and NS group (P>0.05).In terms of IgM content, except for 42 days, there was no significant difference between GA_H group and APS group at other days (P>0.05).At 21 days, there was no significant difference between GA_H group and NS group (P>0.05).【Conclusion】 GA could effectively relieve the immune stress response of Yellow feather broiler chickens induced by LPS stimulation, and enhance the immune regulation ability.

Key words: glycyrrhizic acid(GA); Yellow feather broiler; lipopolysaccharide; immune regulation