Trends in respiratory tract infection treatments in Norwegian cattle: a retrospective register-based study.

Respiratory tract infection (RTI) is a common diagnosis in cattle, particularly in calves, and contributes substantially to antimicrobial use. This study describes the incidence and patterns of RTI treatments in Norwegian cattle, with emphasis on antimicrobial, analgesic and anti-inflammatory drug use. Registry data from 2015 to 2022 were extracted from two national cattle databases, covering more than 67,000 cattle treated for RTI. The annual proportion of herds with at least one RTI treatment increased from 24% in 2015 to 44% in 2022. The median annual number of treatments per affected herd was two. Treatments peaked during winter. On calf level, the probability of receiving at least one RTI treatment by 180 days of age increased from 1.8% to 2.4% over the study period. Median age at first treatment was 52 days. RTI treatments usually involved three or fewer calves (96%), and most animals received only one RTI treatment. Antimicrobials were administered in 96.5% of treatments, most commonly penicillins (β-lactamase sensitive; 54.5%), followed by amphenicols (15.2%) and tetracyclines (7.9%). Short-acting formulations predominated (89.2%). Antimicrobial class changes within 10 days of initial treatment occurred in 13% of calves, typically after four days. Non-steroidal anti-inflammatory drugs (NSAIDs) were co-administered with antimicrobials in 85% of treatments. In conclusion, RTI treatments in Norwegian cattle were widely distributed across herds and increased over time. Treatment practices remained dominated by penicillin, and repeated treatments and changes in antimicrobial class were uncommon. This suggests that narrow-spectrum first-line therapy was generally sufficient in routine RTI management.