Rate of decline of chlorfluazuron concentration in the fat of cattle.

To determine the rate of decline of chlorfluazuron (CFZ) concentration in the fat of cattle. A field depletion study. Fifteen steers that had become contaminated with CFZ through eating cotton trash or cotton leaf pellets derived from CFZ-treated cotton crops. Fat samples were collected from the cattle at about 3 week intervals according to a schedule where each animal was sampled on four occasions up to 340 days after removal from the contaminated feed source. When the effects of dilution are removed CFZ concentrations were found to decline slowly for about 200 days. Depletion was minimal between 200 and 340 days. According to this trial, CFZ-contaminated, nonlactating cattle which have finished growing will remain contaminated. Field experience has not supported this conclusion.