Abstract: The veterinary drug florfenicol is used widely to treat bacterial infections in farmed animals. Long-term intake of foods with florfenicol residues can cause drug resistance, immune suppression and other adverse effects on the body. The aim of this study was to investigate the residual pattern of florfenicol and its metabolite florfenicol amine in the eggs and some body tissues of laying hen fed a diet containing different florfenicol levels, and further develop a predictive model for veterinary drug residues. A total of 250 Roman hens 350 days old and weighing (1.97 ± 0.07) kg at peak production were arbitrarily assigned to five treatments each containing 50 hens, fed a diet supplemented with 0, 30, 60, 120 and 240 mg/(kg mb·d) florfenicol for 5 days, respectively. Eggs were collected every day, and the birds were slaughtered at different times after the termination of drug administration. Egg yolk, egg white, yolk, muscle and liver were collected to measure florfenicol and florfenicol amine concentrations by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results showed that egg production rate was significantly decreased in the 240 mg/(kg mb·d) group from days 1 to 3 after administration compared to the other dose groups (P < 0.05), and returned to that observed in the control group on day 4. The residual levels of florfenicol and florfenicol amine were ranked as follows: egg yolk > yolk > egg white > liver > muscle, and the depletion time was in the decreasing order of egg yolk > yolk > egg white > muscle > liver. The florfenicol dosage and the depletion time as well as the interaction between them had significant effects on the residual amounts of florfenicol and florfenicol amine (P < 0.001), which was depicted by a quadratic polynomial model (P < 0.001). When it was administered to laying hens within the dosage range of 40–60 mg/(kg mb·d) according to the Chinese Veterinary Pharmacopoeia (2015 Version), the depletion time of flurfenicol was 1 day for muscle and liver tissues, 13 days for eggs and 21 days for yolk .

Key words: florfenicol; florfenicol amine; laying hens; eggs; residue; model