Contamination of animal feedingstuffs with nicarbazin: investigations in a feed mill

Some mechanisms of nicarbazin contamination were investigated in a feed mill. Three sequential 3-tonne batches of nicarbazin-free feed were produced directly after a batch of nicarbazin-containing feed (125 mg kg(-1)). Sampling of the nicarbazin-free feed took place at two points before pelleting and at one point post-pelleting. The study was repeated on two further occasions, i.e. three separate nicarbazin-containing feeds and 27 tonnes of 'flushing' feeds were manufactured and sampled in total. Pre-pelleting, the highest nicarbazin concentrations (3.4 +/- 0.26 mg kg(-1)) were observed in the first tonne milled after the nicarbazin containing ration. Thereafter, concentrations steadily declined in successive batches. Post-pelleting samples contained much higher concentrations of the drug. After 8 tonnes had passed through, the concentrations (7.2 +/- 1.29 mg kg(-1)) were between 10 and 20 times greater than the corresponding concentrations detected post-mixing. These concentrations are sufficient to cause violative residues in eggs and broiler liver. The practice of returning post-press sieved material to the pre-press bins was identified as the cause of the problem. Re-routing of sieved material along with better segregation of nicarbazin-containing and nicarbazin-free feedingstuffs markedly reduced the incidence of feed contamination with this compound.