The use of antibiotics to treat dairy calves may result in multidrug-resistant extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli. This study investigated fluoroquinolone and macrolide resistance genes among ESBL-producing E. coli isolated from dairy calves. Fresh fecal samples from 147 dairy calves across three age groups were enriched to select for ESBL-producing E. coli. Plasmid-mediated fluoroquinolone (qnrB), macrolide (mph(A)), and beta-lactam (blaCTX-M groups 1 and 9) resistance genes were identified by PCR and gel electrophoresis in ESBL-producing E. coli. Beta-lactamase variants and antibiotic resistance genes were characterized for eight isolates by whole-genome sequencing. Seventy-one (48.3%) samples were positive for ESBL-producing E. coli, with 159 (70.4%) isolates identified as blaCTX-M variant group 1 and 67 (29.6%) isolates as blaCTX-M variant group 9. Resistance gene mph(A) was more commonly associated with blaCTX-M variant group 1, while resistance gene qnrB was more commonly associated with variant group 9. E. coli growth was quantified on antibiotic media for 30 samples: 10 from each age group. Significantly higher quantities of ceftriaxone-resistant E. coli were present in the youngest calves. Results indicate the dominant blaCTX-M groups present in ESBL-producing E. coli may be associated with additional qnrB or mph(A) resistance genes and ESBL-producing E. coli is found in higher abundance in younger calves.

Veterinarians are being asked to provide more oversight of antibiotics used on dairies and promote stewardship of these drugs because of the risk for development of antimicrobial resistance. As organizations work to develop stewardship guidelines, gathering data on veterinarians' views and actual use can better inform those guidelines. The purpose of this project was to survey dairy veterinarians to understand current antimicrobial use practices and views on antimicrobial resistance. A SO-question online survey was developed and a link sent to members of the Academy of Dairy Veterinary Consultants. The final response rate of 41 % (58 of 143) included only practicing veterinarians. Fifty-nine percent did not believe that the current use of antimicrobials on dairy farms contributed to antimicrobial resistance in human pathogens. Most of the respondents (83 % ) felt that there was unnecessary use of antimicrobials on dairies, particularly in pre-weaned calves, primarily due to protocol non-compliance and farmers' or employees' misidentification of healthy animals as sick and treatment of them with antimicrobials. About half the respondents always had written treatment protocols for their clients, and 40% always provided training on those protocols. Blanket dry-cow therapy was recommended by 65% of the practitioners. The results of this survey provide a baseline of western, large dairy herd veterinary antimicrobial use and recommendations. Responses indicated opportunities for dairy practitioners to improve some antimicrobial stewardship practices that could reduce antimicrobial use.