Antibiotics in 16-day-old broilers temporarily affect microbial and immune parameters in the gut.

Animal health benefits from a stable intestinal homeostasis, for which proper development and functioning of the intestinal microbiota and immune system are essential. It has been established that changes in microbial colonization in early life (the first 2 wk post hatch) impacts the functioning of the adult gut and the associated crosstalk between microbiota and intestinal mucosal cells. The aim of the present study was to study the effect of the administration of antibiotics later in life (d 15 to 20 post hatch) on microbiota and immune parameters. For this purpose, chickens received from 15 d post hatch during 5 d amoxicillin or enrofloxacin through their drinking water. Before and at 6, 16, and 27 d after start of the administration of antibiotics, the composition of the microbiota in the jejunum was determined using a 16S ribosomal RNA gene-targeted DNA microarray, the CHICKChip. At 6 d after the start of the administration of the antibiotics, the composition and diversity of the microbiota were affected significantly (P < 0.05), but this change was small and observed only temporarily since differences disappeared at 16 d after initiating treatment with amoxillin and at 27 d after starting treatment with enrofloxacin. Intestinal morphology and development were not visibly affected since there were no differences between villus/crypt ratios and numbers of PAS+ and PCNA+ cells in the duodenum and jejunum at any time point. At 16 d after the start of antibiotic administration, the number of CD4+ T-cells and CD8+ T-cells in the duodenum was lower compared to the control animals; however, this difference was not significant. At some time points, significant differences (P < 0.05) were observed among the groups to locally expressed IL-8, IL-1β, IFN-γ, IL-2, and IL-4 mRNA. However, this effect was not long lasting, as differences that were observed at 16 d after starting the treatment had disappeared at 27 d after treatment was started. The results of this study indicate that later in the broiler's life, antibiotics only temporarily affect intestinal microbial and immune parameters.