Antibacterial use in Norwegian horses: a nationwide registry-based cross-sectional study

Antibacterials are essential for treating infections in horses, but the use contributes to antimicrobial resistance (AMR), which threatens animal and human health. Despite these concerns, antibacterial use in horses has not been systematically studied and described in Norway, and nationwide registry-based analyses in other countries are scarce. The aim of this study is to describe antibacterial use in Norwegian horses, 2022–2024, by analysing nationwide registry data, with a particular emphasis on gynecological and obstetrical conditions. In addition, we will evaluate the data quality in light of the upcoming EU reporting requirements for data on antibacterial use in horses. A total of 30,362 records reported to the Norwegian Veterinary Prescription Registry (VetReg) were included. Of these, 42.5% were reported by veterinarians and 57.5% by pharmacies. The two most common diagnostic groups treated were skin and hoof conditions and musculoskeletal conditions, accounting for approximately half of all records. Gynecological and obstetrical conditions accounted for 4% of the records. Antibacterial use (in kg active substance) was dominated by oral paste containing the combination of sulphonamide and trimethoprim (> 90% in all three years), followed by injections with beta-lactamase sensitive penicillins. AMEG category D antibacterials (prudent use) accounted for > 99% of the use. These patterns were also observed for gynecological and obstetrical conditions. The completeness of data on antibacterial use in horses in VetReg, in relation to sales data, increased from 75.5% in 2022 to 84.7% in 2024. A higher proportion of AMEG category D antibacterials (> 99%) was observed in our study than in Spain (85%). However, increasing carriage of resistant E. coli in the general horse population suggests that the extensive use of sulphonamide + trimethoprim should be further evaluated. Prudent use could be evaluated to some extent, but the reporting of general organ-related diagnostic codes limited this evaluation. Lack of fully reliable population data for horses limits how differences in antibiotic use between years and countries can be described and evaluated. VetReg data quality for horses was in line with or better than for the species for which data are already reported to the European Medicines Agency.