Effect of lysozyme supplementation on growth performance, immune status, antioxidant function and intestinal microbiota in broilers.

The ban on antibiotic growth promoters (AGPs) has driven the search for green, safe, effective, and sustainable alternatives to enhance the animal health in livestock farming. Lysozyme (LZ) has received widespread attention due to its bactericidal and immunomodulatory functions. However, the effect of different sources of LZ in broilers remains limited. Therefore, this study investigated the effects of recombinant human LZ on the growth performance, immune and antioxidant functions, and microbiome composition of broilers. 450 one-day-old yellow-feathered broilers were allocated into three groups. The chicks were fed a diet supplemented with 0 (LZ0), 250 (LZ250), or 500 mg/kg (LZ500) LZ for 28 d. The data were analyzed by a one-way analysis of variance and polynomial contrasts. Results showed that ADFI showed a linear decrease (P < 0.05) in line with supplemental LZ levels. Serum immunoglobulins and interleukin-10 (IL-10) were increased (P < 0.05), and IL-1β was decreased (P < 0.05) in the LZ500 group, while tumor necrosis factor-alpha (TNF-α) was decreased in the LZ-treated groups (P < 0.001). In addition, the levels of antioxidant enzymes, including glutathione peroxidase (GPX) and superoxide dismutase (SOD), were promoted (P < 0.05), and malondialdehyde (MDA) was reduced in the LZ-treated groups (P < 0.001). The concentrations of propionic, butyric, isobutyric, valeric, and isovaleric acids were increased in the LZ-treated groups (P < 0.01). More importantly, LZ supplementation significantly altered the microbial structure, as indicated by decreased Sellimonas (P < 0.05) and increased Clostridia_vadinBB60 (P < 0.01). Linear discriminant analysis with effect size (LEfSe) plot showed that Faecalibacterium was the predominant bacteria in the LZ0 group. Enterococcus and Ruminococcaceae were dominant in the LZ250 group. In addition, Enterococcus-RF39, Clostridia_vadinBB60 and Sellimonas were enriched in the LZ500 group. In conclusion, dietary LZ supplementation improved the immune status and antioxidant capacity, and stabilized the cecal flora and fatty acids to maintain the health of broilers. This study provides a good basis for the future application of LZ in animal husbandry.