Construction of low intestinal bacteria model and its effect on laying performance and immune function of laying hens

The objective of this study was to establish a low-bacteria intestinal model in chickens, and then to investigate the characteristics involving in immune function and intestinal environment of this model. A total of 180 twenty-one-week-old Hy -line gray layers were randomly allocated into 2 treat-ment groups. Hens were fed with a basic diet (Con-trol), or an antibiotic combination diet (ABS) for 5 weeks. Results showed that the total bacteria in the ileal chyme were significantly dropped after ABS treatment. Compared with the Control group, the genus-level bacteria such as Romboutsia, Enterococ-cus, and Aeriscardovia were reduced in the ileal chyme of the ABS group (P < 0.05). In addition, the relative abundance of Lactobacillus_delbrueckii, Lac-tobacillus_aviarius, Lactobacillus_gasseri, and Lacto-bacillus_agilis in the ileal chyme were also descended (P < 0.05). However, Lactobacillus_coleohominis, Lactobacillus_salivarius, and Lolium_perenne were elevated in the ABS group (P < 0.05). Beyond that, ABS treatment decreased the levels of interleukin-10 (IL-10) and b-defensin 1 in the serum, as well as the number of goblet cells in the ileal villi (P < 0.05). Additionally, the genes mRNA levels of the ileum such as Mucin2, Toll-like receptors 4 (TLR4), Mye-loid differentiation factor 88 (MYD88), NF-kB, IL -1b, Interferon-gama (IFN-g), IL-4 and the ratio of IFN-g to IL-4 were also down-regulated in the ABS group (P < 0.05). In addition, there were no signifi-cant changes about egg production rate and egg qual-ity in the ABS group. In conclusion, dietary supplemental antibiotic combination for 5 weeks could establish a low intestinal bacteria model of hens. The establishment of a low intestinal bacteria model did not affect the egg-laying performance, while caused immune suppression in laying hens.