Background:Accurate estimation of antimicrobial use (AMU) is importantin assessing reduction of agricultural AMU. This cross-sectional study aimedto evaluate several approaches for estimating AMU at the herd level and toreport on AMU for beef and dairy farms in Scotland.Methods:Pharmaceutical sales data for 75 cattle herds (2011-2015) werescreened for antimicrobial products and aggregated by herd and year. Severaldenominators for usage estimates were calculated and compared for theirsuitability at the herd level.Results:The median total mass of active ingredient sold per kg of bovine live-stock was 9.5 mg/kg for beef herds and 14.3 mg/kg for dairy herds. The 'high-est priority critically important' antimicrobials (HPCIA) were by total massof active ingredient, 10.6% of all sales; by total defined daily dose veterinary(DDDVet), 29.8% and by DCDvet, 20.0%. These are the first estimates of AMUfor beef cattle in the UK, and for cattle of any kind in Scotland.Estimates of herd-level usage based on population correction unit (PCU) weresensitive to low values for PCU for specific herd-years due to their demo-graphic composition.Conclusion:Pharmaceutical sales data can provide useful estimates of AMU,but estimating usage per PCU is not appropriate for comparing groups of cat-tle with different demographic compositions or for setting herd-level targets.Total mass of active ingredient per kilogram of livestock is more stable andhence suitable than PCU-based methods for assessing AMU at the herd level