STRATEGIES FOR THE REDUCTION OF ANTIMICROBIALS IN BEEF CATTLE

Antimicrobial use (AMU) in livestock and human medicine is driving antimicrobial resistance (AMR). Both in Europe and US, the increased number of people affected by resistant bacteria infections suggest a need to reduce the misuse or abuse of antimicrobials. Due to the vast negative effects on the health of humans, animals, and the environment, AMR is considered an issue relating to ‘one health’. The aims of this thesis were thus to: i) identify sources of variation in AMU in Italian beef cattle production; ii) investigate the effect of commingling animals from different French farms during batch formation on AMU in Italian fattening farms; iii) explore the role of implementing certain strategies (e.g., quarantine) on the reduction of AMU; and iv) investigate the impact of vaccination against different respiratory pathogens on AMU and animal performance. Chapter 1 reviews the relationships between AMU and AMR, the approaches to monitor AMU, and AMU in livestock species within the context of the Italian-French beef cattle production system, which acts as the case study around which the whole thesis revolves. Chapter 2 investigates sources of variation of AMU in the Italian beef fattening facilities. Chapter 3 addresses the role of commingling animals from different farms during batch formation in French sorting facilities on AMU. Chapter 4 deals with the effect of enforcing quarantine to animals upon their arrival at the fattening units on the mitigation of AMU and animal performance. Finally, Chapter 5 reports the effects of different vaccination strategies and pathogen targets to reduce AMU. Based on the results of the present thesis, AMU has a multifactorial nature, and ‘one health’ approach should be pursued. There is room to reduce AMU in beef cattle through implementation of good on-farm practices (e.g., biosecurity measures, animal welfare, strategies to limit the commingling of animals from multiple sources, appropriate vaccination protocols) and through effective communication among stakeholders, with expected beneficial reductions in AMR. However, at least part of the costs of such strategies should be covered by public bodies to help the farmers in the transition to a more sustainable production.