Residue depletion and withdrawal period determination of fluralaner in edible tissues and eggs following oral administration in laying Hens

To investigate the residue depletion kinetics and establish the withdrawal period of fluralaner in chickens and eggs, a sensitive and reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the quantitative determination of fluralaner residues in edible chicken tissues and eggs. Furthere more, fifty healthy Hy-Line Brown laying hens were selected and received fluralaner solution via drinking water at a dosage of 0.5 mg/kg body weight on the 1st day and 8th day. At 7 days after the final administration, fluralaner residues in all edible tissues declined to levels below their respective maximum residue limits (MRLs). Using WT1.4 software and calculations based on the 95 % confidence interval, the withdrawal periods for fluralaner in muscle, liver, kidney, skin/fat were 12.19, 8.06 10.67 and 4.60 days, respectively. On day 7 after the final administration, the maximum observed fluralaner residue concentration in eggs was 890.72 µg/kg. This level was below the established MRL for eggs (1300 µg/kg) as stipulated by both the Ministry of Agriculture and Rural Affairs of China and the European Union. Moreover, the fluralaner concentration at each time point in eggs remained below 1300 µg/kg at 95 % confidence interval. Considering inter-individual variability, age related metabolic differences, and in reference to the approved withdrawal and egg-discard periods of the originator formulation Exzolt®, a withdrawal period of 14 days was established for the self-prepared fluralaner solution in chickens, while the egg-discard period was determined to be 0 days. Current study provides a scientific and regulatory basis for the rational use of fluralaner in laying hens and supports the establishment of an appropriate withdrawal period and egg-discard strategy in layer production systems.