Mapping antibiotic use and calf-rearing practices in Brazilian dairy farms

Antimicrobial use in preweaning dairy calves is largely driven by the high morbidity and mortality observed in early life and by on-farm management practices. However, such use also contributes to the emergence and dissemination of antimicrobial-resistant bacteria, raising important public and environmental health concerns. This study aimed to characterize antimicrobial use patterns and management practices in Brazilian dairy herds. An online questionnaire was distributed between June and November 2020 via social media, e-mail, and WhatsApp messages to reach dairy farm managers, including producers, farm owners, and professional consultants. After data curation, statistical analyses were performed using multiple correspondence analysis followed by cluster analysis to identify production system typologies. Based on data from 725 dairy farms, 4 clusters were identified, representing a continuum from intensive to low-input systems. Cluster 3 (n = 101) consisted of large, well-structured farms with standardized rearing protocols, regular veterinary oversight, and more judicious antimicrobial use based on clinical signs, although critically important antimicrobials for human medicine were still frequently used. Clusters 1 (n = 205) and 2 (n = 335) represented intermediate systems and included most farms; cluster 1 featured moderately consistent management practices, whereas cluster 2 was characterized by empirical, unsupervised antimicrobial use. Cluster 4 (n = 84) encompassed smallholder farms relying on natural suckling and older-generation antimicrobials such as penicillin. Waste milk feeding was widespread across clusters, particularly in clusters 1 and 2, and was often improperly discarded into sewage systems. In summary, these results reveal substantial heterogeneity in antimicrobial use and management among Brazilian dairy systems. They highlight the influence of veterinary supervision and management quality on antimicrobial decision-making, while emphasizing that larger farms with regular veterinary assistance should consider the World Health Organization's list of medically important antimicrobials to avoid the use of drugs prioritized for human medicine. This study provides an epidemiological baseline to support targeted antimicrobial stewardship and educational strategies tailored to diverse production contexts.