Crufomate residues in milk and milk products following treatment of dairy cows for warble-fly.

Persistence of the organophosphorus pesticide, fenthion, in the milk of ten dairy cows was determined following treatment of the animals for warble fly (a) while at grass, and (b) while housed and fed on silage. The mean concentration of fenthion in the milk of the housed animals was at a higher level for longer after treatment. Following both treatments, the mean fenthion concentration in milk dropped below 0.05 mg kg−1 within 24 h of treatment. No correlation was found between milk yield of cows and total fenthion excreted in milk. The fenthion levels in milk and milk products were determined during a compulsory warble-fly eradication scheme. Low fenthion levels detected in milk after processing were due to the dilution effect of bulking milk. Although the tendency for fenthion to accumulate in the fat fraction in milk resulted in measurable levels of the pesticide in butter and cheese, these levels were below 0.05 mg kg−1.