| Summary: | The present study was conducted to investigate the influence of fermented Broussonetia Papyrifera (FBP) on growth performance, intestinal antioxidant capacity, inflammation and microbiota of grass carp. Fish (initial weight: 50.0 ± 0.5 g) were fed diets with 0 (control diet), 5 % (FBP5), 10 % (FBP10), 15 % (FBP15) and 20 % (FBP20) of FBP supplementation respectively for 8 weeks. The results showed that FBP5 group significantly decreased FCR of grass carp (P < 0.05). Besides, FBP supplementation significantly decreased intestine Cu/Zn SOD activity (P < 0.05), as well as significantly elevated mRNA expression level of kelch-like-ECH-associated protein 1 (keap1) and depressed mRNA expression level of NF-E2-related factor 2 (nrf2), superoxide dismutase 1 (sod1) and catalase (cat) (P < 0.05). The content of malondialdehyde (MDA) increased significantly in the FBP20 group compared to the control diet (P < 0.05). The expression level of interleukin-8 (il-8) and interferon γ (ifnγ) downregulated with increased dietary FBP, and significant difference was found in FBP20 group (P < 0.05). In addition, when the supplementation of FBP was no more than 15 %, the abundance of Firmicutes and Fusobacteria increased significantly, while the abundance of Actinobacteria and Cyanobacteria decreased significantly in intestine of grass carp (P < 0.05). Compared to the control diet, the richness and diversity of intestinal microbiota of grass carp decreased significantly in FBP20 group (P < 0.05). According to the second order polynomial regression equation analysis of SGR and FCR, the optimal additional level of FBP was estimated to be 4.58 % and 5.28 %, respectively. The recommended maximum addition of FBP in diet of grass carp was up to 15 % according to the results of intestinal microbiota.
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