Turbidimetric assay for virginiamycin in feeds and premixes

A turbidimetric assay method applicable to virginiamycin at level ranging from 5 g/ton in feeds to 50% in a premix is described. Incubation period is 4 h. Test organism is Streptococcus faecium ATCC 8043. On 6 levels of feed-grade material, the overall mean recovery was 6.75% Standard recovery studies resulted in RSD values ranging from 2.01 to 3.88% and a mean standard recovery of 100%.