Deposition and depletion of the coccidiostats toltrazuril and halofuginone in eggs

Toltrazuril (TZ), a triazinetrione derivative, and halofuginone (HFG), a quinazolinone derivative, have been licensed for the prevention and treatment of coccidiosis in broilers and turkeys, but have been excluded for use in laying hens. Little is known regarding the deposition of residues of toltrazuril and halofuginone in eggs and their rate of depletion. In this study, laying hens were treated with therapeutic doses of TZ (78 mg l−1 in the drinking water for 2 days, repeated after a 5-day interval for another 2 days) and HFG (3 mg kg−1 in the feed for 14 days). Eggs were collected before, during and after treatment. Residue concentrations of toltrazuril and its metabolite ponazuril (PZ) and halofuginone were determined in whole egg, as well as in the yolk and albumen. TZ and PZ residues were monitored daily in whole egg until 19 days post-treatment. PZ was found the predominant residue formed. Toltrazuril concentrations in whole egg reached a maximum during treatment of 1500 μg kg−1, while ponazuril concentrations increased to 11,000 μg kg−1. At the end of the post-treatment period levels for TZ in whole egg had dropped below the limit of detection (LoD) of 30 μg kg−1 but PZ was still present at 1600 μg kg−1 (LoD: 10 μg kg−1). Residues of TZ and PZ were mainly distributed in the egg yolk. HFG residues were monitored until 14 days post-treatment. Halofuginone was detected in egg up to a concentration of 450 μg kg−1 during the medication period and declined fairly rapidly after the end of administration. After 12 days withdrawal, residue levels reached the limit of detection of 2 μg kg−1. Residue concentrations of HFG in yolk were approximately twice that in albumen.