Florfenicol can inhibit chick growth and lead to immunosuppression

Florfenicol (FLO) is a chemically synthesized broad-spectrum antimicrobial agent of amide alcohols for animals, which is one of the most widely used antimicrobials in livestock, poultry, and aquaculture. With the use of FLO, more and more attention has been paid to its hematopoietic toxicity, immunotoxicity, genotoxicity, and embryotoxicity. In this study, SPF chicks at the age of 3 d began to drink water with the FLO at a dose of 100 mg L^–1 for 6 consecutive days, and the growth performance of chicks was monitored, the effect of FLO on immune organs was detected by pathological examination and TdT-mediated dUTP nick-end labeling (TUNEL) apoptosis staining. In order to evaluate the level of organism immunity, the level of Newcastle disease virus antibody in serum was detected by hemagglutination inhibition test, the content of cytokines (IL-1, IL-2, IL-6, TNF-α, IFN-γ) in serum was detected by enzyme linked immunosorbent assay (ELISA), and the transcription of interferon-related genes (IRF-7, 2´-5´OAS, Mx1) and cytokine genes (IL-6, TNF-α, IFN-γ) in immune organs were detected by real time fluorescence quantitative PCR. The results showed that the early application of FLO could inhibit the growth and development of chicks, and the body weight and immune organ index of the treatment group were lower than those of the control group. Histopathological examination showed that there was a decrease in the number of lymphocytes in the bursa of Fabricius in the treatment group in the early stage of drug withdrawal, and the results of TUNEL apoptosis staining in the bursa of Fabricius showed that obvious lymphocyte apoptosis occurred in the FLO treatment group. Compared with the control group, the transcription levels of interferon-related genes IRF-7, 2´-5´OAS, and cytokine genes IL-6, TNF-α and IFN-γ in FLO treatment group decreased to a certain extent, while the transcription level of Mx1 gene had no significant difference at all time points. The level of serum Newcastle disease virus (NDV) antibody and the contents of cytokines IL-1, IL-2 and IFN-γ in the FLO treatment group were significantly lower than those in the control group in the early stage of drug withdrawal, but recovered gradually in the later stage. This study showed that FLO has a certain degree of effect on the immune function of chicks, and the results of the study laid the foundation for further research on the mechanism of FLO-induced immunotoxicity.