Short communication: Correlation of on-site inspection and laboratory milk testing results for Wisconsin grade A dairy farms in 2007 and 2008

This study examined whether regulatory on-site dairy farm inspection results correlated with reported laboratory somatic cell count (SCC), standard plate count (SPC), and β-lactam drug residue (DR) results for individual farms. Results were obtained for Wisconsin grade A dairy farms in 2007 and 2008 (>11,000 farms, >1.4 million data points). The proportion of farms failing an on-site inspection ranged from 12% for farms that had never failed an SCC test (>750,000 cells/mL), an SPC test (>100,000 cfu/mL), or a DR test (drug detected) to 55% for farms that had failed at least 1 of each type of test. Conditional probability analysis showed that the probability of a farm failing an on-site farm inspection was higher if the farm had failed a DR test and increased as the proportion of samples failing SCC or SPC or both increased. However, the statistical correlations were weak (R ≤ 0.22) between on-site farm inspection result (pass/fail) and numerical or logarithmic SCC or SPC or pass/fail DR result. The weak correlation may reflect temporal and methodological differences between on-site farm inspection and laboratory testing and may indicate that they provide different but useful indices of milk safety and quality. Alternatively, the results suggest that examination of a different frequency and focus for on-site farm inspection is warranted.