Rapid screening of narasin residues in poultry plasma by time-resolved fluoroimmunoassay

A simple and rapid time-resolved fluoroimmunoassay (TR-FIA) method has been developed for the screening of narasin in poultry plasma. This method involves only a dilution of sample and competitive microwell plate immunoassay combined with the measurement of time-resolved fluorescence. The performance of the assay has been confirmed by validation according to Commission's Decision 2002/657/EC. Decision limit and detection capability of the assay have been 1.2 and 1.5 ng ml−1, respectively. Narasin recovery from plasma has ranged from 101.0 to 121.3%. In the feeding study broiler chickens have been fed narasin at a dose rate of 0, 3.5 and 70 mg kg−1 feed for 3-week period and the concentration of narasin in the plasma and muscle of broilers have been studied by the TR-FIA. Feeding with 70 mg kg−1 and no withdrawal period resulted in a very high narasin levels in blood, and the artificial contamination level of feed (3.5 mg kg−1) was also detected by the analysis of blood samples. A relationship was observed between the concentrations of narasin in plasma and breast muscle (R2 = 0.83) and leg muscle (R2 = 0.90). These results suggest that the analysis of poultry blood samples could be used as a predictor of narasin residues in muscle.