The aim of this study was to identify variables associated with antimicrobial drug use for bovine mastitis. Intramammary tubes used for lactating cows, discarded by farm personnel, were collected in dedicated trash bins for 12 months on each of 104 herds (Michigan n = 49, Pennsylvania n = 55). Antimicrobial use was quantified using two metrics: arithmetic (number of discarded tubes) and defined daily dose (DDD) per 1,000 cow-days. Mastitis control practices, attitudes, and behaviors were also collected using a survey of herd owners and managers conducted during herd visits. Additionally, a human resources questionnaire survey about dairy producers/manager’s beliefs and practices regarding employee communications, training, and education was also collected for each herd. Across all herds, intramammary tube use based on arithmetic count was 4.43 tubes per1,000 cow-days and 3.52 per 1,000 cow-days based on DDD. A higher trend of antimicrobial use (5.22 tubes per 1,000 cow-days and DDD of 4.1 per 1,000 cow-days) was found in Pennsylvania than in Michigan (3.61 tubes per1000 cow-days and the DDD 2.91 per 1,000/ cow-days). Ranking of antimicrobial use showed that ceftiofur was the most frequently used antimicrobial in the study, followed by cephapirin, pirlimycin, amoxicillin, hetacillin, and cloxacillin. A majority of producers believed that they had sufficient knowledge of mastitis treatment and control, but only 23% of them had a written treatment protocol, and less than half of them (44%) reviewed animal health? History before treating infected cows. Moreover, 80% disagreed that culture of milk samples is needed to make mastitis treatment or management decisions. Multivariate models had similar results, regardless of the metric used to determine intramammary drug use; there was a positive correlation between drug use and the new subclinical mastitis rate (based on monthly DHI SCC testing) and the producer’s willingness to improve the image of the dairy products. Use of natural remedies for mastitis treatment was negatively correlated with intramammary drug use. Our results indicate that there continues to be a gap between producer practices and beliefs and best practices to reduce antimicrobial use on dairy farms. Also, intramammary drug use is highly associated with the dynamics of subclinical mastitis as measured in individual cows, and a herd average level.
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