Possible causes of nicarbazin residues in chicken tissues

Two experiments were carried out to investigate possible causes of nicarbaz in residues in broiler chicken tissues. The first experiment was designed t o establish whether feeding nicarbazin as stipulated in the product licence can result in 4,4'-dinitrocarbanilide (DNC) tissue residues exceeding the JECFA MRL (200 mug/kg). It was shown that the MRL was exceeded in the liver s of broilers housed on deep litter, but not in those of broilers housed on wire flooring. Muscle DNC concentrations were well below the MRL. The high er residual tissue concentrations in birds housed on deep litter were attri buted to faecal recycling. The second experiment was to establish the relat ionship between nicarbazin-contaminated withdrawal ration up to the point o f slaughter and DNC residues in the tissues of broilers that had not been p reviously exposed to nicarbazin. Tissue DNC concentrations were found to be proportional to feed concentrations. The housing method caused no signific ant difference in tissue residues. Meal containing nicarbazin at a concentr ation of 2.4 mg/ kg or greater caused liver DNC residues above the JECFA MR L. Violative residues may, therefore, occur in chickens not exposed to nica rbazin during rearing, but fed withdrawal ration contaminated at 2.4 mg/ kg or greater, or in chickens housed on deep litter and fed nicarbazin-medica ted meal according to the product licence even when the withdrawal ration i s nicarbazin-free.