Effects of dietary Zanthoxylum bungeanum seed powder on growth performance, immune function, and cecal microbiota in broilers

This study was conducted to evaluate the effects of Zanthoxylum bungeanum seed powder (ZBS) on growth performance, immune function, and cecal microbiota in 817 broilers. A total of 260 one-day-old 817 broilers were randomly assigned to 4 treatment groups (CON, ZBS1, ZBS2, and ZBS3) with 5 replicates per treatment and were fed diets containing 0, 1%, 2%, or 3% ZBS, respectively, for 63 d. The results showed that dietary ZBS had no significant effects on average daily feed intake, average daily gain, or gain-to-feed ratio (P > 0.05). However, body weight at 28 and 63 d and average daily gain during d 1–28 and d 1−63 showed significant quadratic responses to increasing dietary ZBS levels (P < 0.05). The bursa of Fabricius index increased linearly with increasing ZBS inclusion (P < 0.05). Serum concentrations of IL-2, IL-6, TNF-α, IgA, and IgG and splenic contents of IgA, IgG, C3, and C4 were significantly increased (P < 0.05), whereas splenic IL-1β content and the expression of TLR4/MyD88/NF-κB pathway-related genes was significantly decreased (P < 0.05). 16S rRNA sequencing showed that ZBS did not affect cecal microbial α-diversity (P > 0.05), but altered microbial community composition. The relative abundances of Faecalibacterium, Bifidobacterium, and Megasphaera were significantly increased in the 3% ZBS group (P < 0.05). PICRUSt2 analysis indicated that the predicted abundances of starch and sucrose metabolism, carbohydrate metabolism, the phosphotransferase system, and pyruvate-formate lyase-related functions were significantly increased in the 3% ZBS group (P < 0.05). Redundancy analysis showed that microbial community variation was significantly associated with dietary ZBS level and immune-related parameters, including IgA, IgG, C3, and C4 (P < 0.05). In conclusion, dietary ZBS improved humoral immunity-related parameters, reduced the expression of inflammation-related genes in the spleen, and affected the composition and predicted functions of the cecal microbiota in broilers. Based on quadratic regression of splenic C4, IL-1β, TRAF2, TLR4, and NFKB2, the optimal dietary ZBS inclusion level was estimated at 1.00−2.55%.