Dietary Bazhen San solid-state fermentation product improves laying performance, immunity and intestinal health in laying hens during the late laying period

The aim of this study was to investigate the effects of solid-state fermentation products of Bazhen San (FB) on the production performance, immunity, and intestinal health of laying hens during the late laying stage. A total of 150 70-week-old laying hens were randomly assigned to five treatment groups, with five replicates per group and six hens per replicate. The control group (CON) was fed a corn–soybean meal-based diet, whereas the other four treatment groups were supplemented with 0.3% FB (LFB), 0.6% FB (MFB), 0.9% FB (HFB), and 0.6% unfermented Bazhen San (BZ), respectively. The results showed that, compared with the CON group, all treatments significantly increased the egg production rate and reduced the feed-to-egg ratio ( P < 0.05). Moreover, the effect in the MFB group was significantly greater than that in the BZ group ( P < 0.05). In terms of egg quality, the MFB and HFB groups significantly improved yolk color and Haugh units ( P < 0.05). Regarding immune function, serum immunoglobulin A (IgA) levels were significantly increased in all treatment groups ( P < 0.05), whereas interleukin-1β (IL-1β) and interleukin-6 (IL-6) concentrations were significantly decreased ( P < 0.05). The MFB and HFB groups also significantly increased serum immunoglobulin G (IgG) levels ( P < 0.05), as well as jejunal and ileal secretory immunoglobulin A (sIgA) levels ( P < 0.05). In addition, serum IgG levels in the MFB group were significantly higher than those in the BZ group ( P < 0.05). In terms of intestinal health, FB treatment significantly enhanced antioxidant enzyme activity in the jejunum and ileum, reduced malondialdehyde (MDA) content, improved intestinal morphology. The microbiome analysis of the cecum showed that FB improved the abundance of beneficial bacteria in the intestine. Spearman correlation analysis revealed that the relative abundance of Odoribacter and Enterococcus was positively correlated with serum IgA levels and negatively correlated with IL-6 concentration. Therefore, dietary supplementation with FB can improve intestinal health, and systematically improve the immune status of the body, thereby promoting the health of laying hens during the late laying stage and improving production performance, dietary 0.6% to 0.9% FB inclusion is suggested.