Farm-Level Antimicrobial Surveillance and Year-to-Year Changes in Antimicrobial Use Intensity in the Pig Sector: Evidence from Hungary’s National Monitoring System

Background/Objectives: Farm-level monitoring of antimicrobial use (AMU) is essential for mitigating antimicrobial resistance (AMR) within a One Health framework because aggregated sales data cannot identify farms and production stages with high AMU. This study evaluated year-to-year changes in AMU intensity and antimicrobial-class distribution in a longitudinal cohort of 492 large-scale Hungarian pig farms in 2023 and 2024 and identified priorities for antimicrobial stewardship. Methods: Mandatory veterinarian-reported AMU data were analyzed retrospectively. The same 492 farms were included in both years, representing approximately 3.7 million pigs in 2023 and 3.8 million in 2024. AMU intensity was expressed as milligrams of active substance per kilogram of pig biomass using the standard live weights specified in the European Medicines Agency’s ESUAvet methodology: 120 kg per slaughter pig and 240 kg per breeding sow. Antimicrobials were grouped by Antimicrobial Advice Ad Hoc Expert Group (AMEG) category. Results: In the 492-farm cohort, AMU intensity was 5.1% lower in 2024 than in 2023 (55.0 versus 57.9 mg/kg biomass). Category B intensity decreased in all farm categories; Category C increased on only-fattener and breeding farms but decreased on farrow-to-finish farms; Category D remained dominant. AMU was concentrated in specific production stages and farms: 57.5–86.4% of breeding-unit AMU was reported for post-weaning pigs, the 20 farms with the highest absolute use accounted for 43.3% of total cohort AMU, and the 20 farms with the highest absolute Category B use accounted for approximately 68.8% of cohort Category B use. Oral formulations represented 93% of reported antimicrobial quantity. Medicated-premix use decreased by approximately 25%, while drinking-water and injectable formulations increased. Conclusions: Mandatory farm-level surveillance provides data for benchmarking and targeted stewardship. Interventions should distinguish absolute use from biomass-adjusted intensity and focus on farms with disproportionate use and the post-weaning phase. The observed 2023–2024 difference is descriptive; additional years of data are needed to assess longer-term patterns in AMU intensity.