VALIDATION-STUDY OF ASSAY FOR NEOMYCIN IN FEED

The neomycin microbiological cylinder plate assay using an ionic extra ction method was validated for 2 swine feeds with neomycin base concen trations of 140.0 and 280.0 g/ton, 2 cattle feeds with neomycin base c oncentrations of 140.0 and 280.0 g/ton, and 2 premixes with neomycin b ase concentrations of 1.4 and 7.0 g/b. The accuracy, precision, and re producibility were evaluated by assaying the 6 feed samples in duplica te on 6 different days by an Upjohn laboratory (Laboratory I)and 2 out side laboratories (Laboratories 2 and 3) for a total of 72 data points per laboratory. Three plates were used for each sample assayed. The r ecovery over all complete (type C) feed samples and (type B) premixes tested, ranged from 82 to 109% for Laboratory 1, 85 to 114% for Labora tory 2, and 78 to 134% for Laboratory 3. Mean percent recoveries for a ll samples tested were 98.0, 98.9, and 103.7% for Laboratories 1, 2, a nd 3, respectively. Day-to-day performance yielded 95% confidence limi ts of +/-11.9, +/-16.9, and +/-25% for Laboratories 1, 2, and 3, respe ctively. Of 215 assay values, 206 (96%) fell within 20% of the actual targeted recovery (100%). Plate-to-plate variation of each of the 3 la boratories also was assessed. Statistical estimates for the use of 1, 5, and an infinite number of plates showed that when 2 plates were use d by Laboratories 1, 2, and 3, than 99, 99, and 95%, respectively, of the assay results fell within the acceptable assay compliance limits ( 70-125% recovery) for complete feeds and premixes. Slight improvement was found only for Laboratory 3, when more than 2 plates were used.