Fipronil administration in laying hens: tissue residue profiles and wihtdrawal-time estimation

Abstract

Fipronil (FIP) is a pyrazole insecticide authorized to control ectoparasites in small animals(worldwide) and cattle (in some countries). Few approved antiparasitic compounds are available forpoultry. As consequence, the extra-label use of FIP has been described in this species to control thered mite Dermanyssus gallinae, an ectoparasite that constitutes an important health problem withhuge economic repercussions in poultry production. Since FIP and its fipronil sulfone (FIP-SO2)metabolite residue profiles in eggs after administration to laying hens have been reported, the maingoal of the current study was to investigate the FIP and the FIP- SO2 metabolite residues profiles inedible and other tissues after extra-label administration in laying hens. Hens were treated extralabelled with FIP (ECTOLINE® 1%) in feed and via topical application. Following animal welfarestandards, the hens were slaughtered at different times within a 60-day post-treatment period. Plasma,muscle, liver, kidney, fat, skin, feathers, and feces samples were collected and analysed to quantifyFIP and FIP- SO2 residues by UFLC-MS/MS. The withdrawal period was estimated by linearregression analysis of the log residual concentrations (fipronil+fipronil-SO2) measured in edibletissues vs. time of the terminal elimination phase. The Maximum Residue Limits (MRLs) establishedfor this species related to fipronil use as a pesticide were considered for the calculations. FIP and FIPSO2 residues were quantified in all tissues following both routes of administration. The FIP-SO2residues were the highest in most tissues. After oral administration, FIP was quantified mainly infeathers (maximum residue level [Cmax] of 0.24±0.16 µg/g at 9 days post-treatment [tmax]), and fat(Cmax= 0.49±0.46 µg/g; tmax= 6 days). The highest FIP-SO2 residue profiles were found in fat (Cmax=9.9±4.2 µg/g; tmax= 15 days), skin (Cmax= 1.7±0.6 µg/g; tmax= 9 days), and liver (Cmax= 1.1±0.5 µg/g;tmax= 6 days). Meanwhile, after topical administration, the highest residues were for FIP in feathers(Cmax: 17.6±5.3 µg/g) at 5 days post-treatment. High FIP-SO2 residues were also quantified in feathers(Cmax: 2.2±1.7 µg/g; tmax= 5 days), fat (Cmax: 1.8±0.8 µg/g; tmax= 15 days), and skin (Cmax: 0.44±0.1 µg/g; tmax= 15 days). Fipronil marker residue profiles following both administration methods exceeded tolerances and MRLs in poultry tissues. Fortunately, the lowest residue levels were found in the main edible tissue, the muscle (meat), in both administration methods. However, the estimated withdrawal periods were long and economically impractical. In poultry production, it is crucial to consider that laying hens reaching the end of their productive period are intended for consumption. These results show that the consumption of edible tissues from treated chickens could pose undesirable health effects. Fortunately, low concentrations were found in muscle. Future studies applying the risk analysis tool will be necessary to determine if there is a potential risk to consumers.