Antibiotic residue prevention methods, farm management, and occurrence of antibiotic residues in milk.

The objective of this study was to determine associations among the occurrence of antibiotic residues in bulk milk and various farm management practices. Ninety-four dairy farms were visited after antibiotic residues were detected in samples of their bulk milk (case farms) along with an equal number of residue-free farms (controls). Farmers completed questionnaires designed to elicit details of management practices used on farms and methods employed for prevention of antibiotic residues. Factors were initially examined unconditionally for statistical association with occurrence of residues; then multivariate associations were determined using multiple logistic regression. After adjusting for herd size in a logistic model, the risk of residues in milk was observed to increase in association with the frequent use of part-time labor in the milking of cows. The risk of residue occurrence was decreased in association with the use of milk residue test kits, when the farmer believed that increasing the dose of antibiotic required an increase in the withholding time of milk, and when tie stall and pipeline milking systems were used rather than milking parlors or tie stall and dumping station systems.