Impact of bovine respiratory disease on lung lesions, slaughter performance and antimicrobial usage in French beef cattle finished in North-Eastern Italy

Bovine respiratory disease (BRD) is a major health concern in beef cattle, with several pathogens and environmental risk factors being involved. Clinical signs of BRD may remain undetected, preventing proper diagnosis. Yet, BRD-associated lung lesions can be detected at slaughter, providing a more sensitive way to estimate BRD prevalence, as these lesions are present also in subclinically affected animals. In April–August 2016, the lungs of 518 Charolaise males from 8 farms in North-Eastern Italy were scored at slaughter based on the presence of pleural adhesions and the percentage of affected parenchyma. Moreover, individual antimicrobial dosages were acquired from the farm registries. 64% of animals had at least one lung lesion; a negative association between lung lesions and carcass weight was found. No association between lung lesions and antimicrobial use was identified. The appropriateness of each antimicrobial treatment was evaluated based on the ratio between each actual daily dose used and the correspondent defined daily dose available in the Summary of Product Characteristics (SPC). Three methods based on different estimation of live-weight-at-treatment were applied and provided significantly different results for some antimicrobial classes. Aminoglycosides and high-priority critical antimicrobials like macrolides were those most frequently administered (20% and 42% of treatments, respectively). Evaluation of dosage appropriateness showed that aminoglycosides were administered properly in 60–75% of treatments, while macrolides were underdosed in 30–60% of treatments. In conclusion, this study shows a high prevalence of BDR-associated lung lesions at slaughter associated with carcass weight, and that antimicrobial use is frequently inconsistent with recommended doses