Antibiotic consumption is a major driver of antibiotic resistance in calves raised on Italian cow-calf beef farms

Although its importance, little information is available on antibiotic-resistance in cow-calf beef farms. This study aimed to determine prevalence and risk factors for antibiotic-resistant organisms in this livestock system. Fifty-four farms from Central Italy were included to assess the presence of antibiotic-resistant indicator Escherichia coli and of ESBL and/or AmpC-producing E. coli (ESBL/AmpC-EC) in calves. Antimicrobial usage (AMU) was recorded, and farm-related variables were collected through questionnaires. Potential risk factors were tested using a mixed-effects logistic regression model. The presence of resistant-E. coli was recorded in 75.9% of farms (95% confidence interval [CI]: 62.4-86.5) with resistance to tetracyclines, sulfonamides, penicillins, and fluoroquinolones as the most frequent. The prevalence of farms positive for ESBL/AmpC-EC was 35.2% (95% CI: 22.7-49.4). AMU on the farms originating a resistant-E. coli was higher than that on the farms originating a susceptible-E. coli. The same difference was found for the consumption of beta-lactams (beta-DCD/year) and AMU via the parenteral route, which resulted also associated with the presence of ESBL/AmpC-EC. Farms with higher beta-DCD/year had an increased risk of being positive for resistant-E. coli, whereas farms with higher overall AMU had an increased risk for ESBL/AmpC-EC presence. Among farm-related factors, only farm size was associated with the presence of ESBL/AmpC-EC (odds ratio: 5.8, 95% CI: 1.3-26.3).Our findings highlight a reduction of the risk of ESBL/AmpC-EC in small cow-calf farms, and a strong association between AMU and antibiotic-resistance. Antibiotic stewardship programs are needed to improve the health status of cow-calf farms and ensure their long-term sustainability.