Lactobacillus Salivarius SNK-6 Activate Intestinal Mucosal Immune System of Laying Hens by Regulating Cecal Microbial Community

The production performance and disease resistance of laying hens decrease obviously with age. Lactobacillus spp., which is generally considered a kind of beneficial bacteria in the intestine, can compete with pathogenic bacteria to regulate the balance of intestinal microflora and host immunity. However, how Lactobacillus salivarius (L. salivarius) SNK-6 impacts intestinal microbial communities and the relationship between gut microbiota and host immune responses remains unclear. This study aimed to investigate the effects of supplemental L. salivarius SNK-6 on laying performance, the immune-related genes expression in cecal tonsil, as well as the cecal microbial composition of laying hens. Here, 384 Xinyang black commercial hens (55 weeks old) were randomly allocated to three groups: basal diet (Con), the low L. salivarius SNK-6 group (T1: 1*106 CFU/g), and the high L. salivarius SNK-6 group (T2: 1 * 107 CFU/g). The results showed that the feed intake and broken-egg rate in the T1 group were significantly higher than the Con group (P <0.05). Meanwhile, TLR-mediated immune response (TLR-6, MyD88, NF-kB, IL-1beta, IL-10, and IL-12) and MHC-mediated immune response (MHC-II, CD80, CD86, CD40L, CD40, and CD28) were significantly upregulated. 16S rRNA gene sequencing indicated that supplemental L. salivarius SNK-6 had no significant difference on Alpha -diversity and only displayed a trend difference in Beta -diversity of cecal microbiota (P = 0.07). LEfSe and Random Forest were further used to identify bacteria family Enterobacteriaceae, order RF39, genera Ochrobactrum, and Eubacterium as biomarkers between Con and T1 group. Genera Ochrobactrum, which had high relative abundance and nodal degree in T1 and T2 groups, showed a significant positive correlation with the expression of TLR-6, IL-10, MHC-II, and CD40 in cecal tonsil might play a critical role in activating the host intestinal innate immune responses. Overall, dietary supplemental L. Salivarius SNK-6 can play an immunomodulatory role by regulating cecal microbial composition. However, the changes in immune responses may be at the expenditure of corresponding production performance, which needs to be weighed in practical application.