The effect of shiitake mushroom bran on the immune regulation mechanism and microbial community of broiler chickens.1440 AA broiler chickens were randomly divided into 4 groups,with 9 replicates in each group and 40 chickens in each replicate.0%,1%,2%,and 4%of Flammulina velutipes mushroom bran were added to the basic feed as experimental feed for each group,and the experiment lasted for 14 days.The results showed that,Compared with the control group,Group Ⅲ broiler chickens showed a significant increase in body weight by 2.10%(P<0.05)at 14 days,a significant increase in total weight gain by 3.72%(P<0.05)from 7 to 14 days,a significant increase in total weight gain by 2.33%(P<0.05)from 1 to 14 days,and a significant decrease in feed to meat ratio by 3.26%(P<0.05)from 7 to 14 days;In addition,there was no significant difference in the total food intake of broiler chickens among the treatment groups(P>0.05).The liver index of Group Ⅲ broiler chickens significantly increased on the 7th and 14th day(P<0.05),and the thymus index of Group Ⅱ and Ⅲ broiler chickens significantly increased on the 14th day(P<0.05).On the 7th day,the serum immunoglobulin G(IgG)content in Group Ⅲ broiler chickens significantly increased(P<0.05),while the levels of tumor necrosis factor alpha(TNF-α)and interferon-γ(IFN-γ)were significantly downregulated in Group Ⅱ(P<0.05);On the 14th day,the serum IgG levels of broiler chickens in groupsⅡ and Ⅲ significantly increased(P<0.05),while the levels of TNF-α and IFN-γ significantly decreased(P<0.05).The Shannon index and Chao1 index of cecum in Group Ⅱ and Ⅲ broiler chickens were significantly increased(P<0.05).(Experimental conclusion)Supplementing with 4%shiitake mushroom bran can promote the development of immune organs,improve serum immune indicators,and ultimately promote the growth and development of broiler chickens.