Drug residues in dairy cattle industry: epidemiological evaluation of factors influencing their occurrence.

A random study of 3000 dairy farmers was designed to determine 1) management factors that may be associated with the occurrence of drug residues; 2) the dairy farmers' attitudes and knowledge about residues; 3) how these variables influence the occurrence of residues in dairy cattle. Management factors perceived as having the greatest influence on drug residues in milk were insufficient knowledge about withdrawal periods, errors due to hired help, insufficient identification and record of animals treated for mastitis, metritis treatment, dry cow treatment for mastitis, and not reading the label. Forty-one percent of farms with residue problems used medicated feeds compared with 38.9% of control farms. Factors significantly associated with the occurrence of residues were herd size, increased number of hired persons, increased frequency of use of medicated feeds, category of medicated feed, and producer's attitude toward the public health significance of residues. Farmers needed more information in five areas: likelihood of persistent residues from various types of chemicals (26.8%), consequences of chemicals occurring in livestock products (22.4%), withholding times for specific chemicals (20.4%), disposal of surplus farm chemicals (17%), preparation of products for use in livestock (13.4%).