Microbiological Assay of Monensin in Chicken Rations

Abstract

Abstract The microbiological plate assay method for monensin in chicken rations reported earlier was submitted in a slightly modified form to 10 collaborating laboratories, along with randomized and coded samples. Other factors in the experiment design were ration types (4 at 2 potency levels) and feed forms (2—meal and pellets). Mean recoveries on 4 ration types were 90.5–96.3% of label over all laboratories and feed forms, while mean recoveries on the 2 feed forms were 96.7% for meal and 89.7% of label for pellets over all laboratories and ration types. The mean recoveries in the 10 laboratories ranged from 78.6 to 119.9% of label, with a median of 93.8%. Only one laboratory was an outlier. There were no significant interactions. The laboratories were uniform with respect to within-laboratory variation. Relative standard deviations of the assay within the laboratories ranged from 3.5 to 12.5% with a median of 6.85%. The microbiological assay method for monensin has been adopted as official first action.