Effect of mixing animals in France on the use of antimicrobials in Italian beef fattening farms

Since their discovery, antimicrobials have contributed to treat infectious diseases. However, several studies have highlighted an association between antimicrobial use (AMU) and the development of antimicrobial resistance, a threat to both human and animal health. Italy is the main European importer of young beef bulls and heifers from France. Before transportation to Italy, animals are collected by exporter companies from farms located across the country and mixed. The practice of mixing animals from different farms is known for its negative effects on animal health and welfare, such as the increased incidence of bovine respiratory disease. The aim of this study was to investigate the effect of the initial mixing of beef cattle in France on AMU in Italian fattening farms. The study was carried out using the information of 25 Italian specialised beef fattening farms associated with a producer organization of Veneto region (AZoVe, Cittadella, Italy), and included approximately 50,000 male and female animals of Charolaise and Limousine breeds imported from France from 2015 to 2018. In vivo performances and information on animal ID, a number of treatments administered per animal and amount of antimicrobial per treatment (ml) were available. A treatment incidence of 100 (TI100) per animal was calculated to quantify AMU. Each animal belonged to a batch defined as a group of individuals of the same breed and sex and similar entry body weight in the fattening farm. To investigate the effect of mixing on AMU, each batch was assigned to 1 of 6 classes created according to the French province of origin. Specifically, class 1 contained batches of animals collected from 1 province only, and so on up to 6 provinces. Data were analysed using the software SAS 9.4. Overall, males were more treated than females (TI100: 4.15 vs. 3.56; p < .05), and Limousine tended to receive more treatments than Charolaise (TI100: 4.06 vs. 3.62; p=.09). The highest T100 was observed in autumn and the lowest in spring (3.98 vs. 3.62; p < .05). The practice of mixing animals from different provinces was significant in explaining the variation of AMU (p < .05), with class 1 having lower TI100 compared to other classes; this suggests that reducing a priori the number of provinces where animals are originally collected may contribute to decreasing AMU in beef production.