Biosecurity implementation in indoor and outdoor-access broiler production systems in the Netherlands

Good biosecurity practices on poultry farms can improve animal health, welfare, and productivity, but implementation varies considerably between farms. Recurrent highly pathogenic avian influenza (HPAI) outbreaks and the expansion of higher-welfare systems with outdoor access have raised concerns about potential differences in exposure risk. However, it remains unclear to what extent biosecurity implementation differs between production systems. A cross-sectional comparative study was conducted to assess HPAI-related biosecurity practices and risk factors in Dutch broiler farms, comparing intensive systems (indoor-only) and extensive systems (slower-growing broilers with covered outdoor access). The study included 78 farms (63 intensive and 15 extensive). Biosecurity was assessed using a harmonized subset of the Biocheck.UGent survey. From 40 comparable variables, 28 were selected based on relevance to HPAI introduction and transmission pathways. Differences between production systems were evaluated using Bayesian logistic regression with horseshoe priors. Most biosecurity measures did not differ substantially between systems, with considerable variation observed within both intensive and extensive farms. The largest estimated differences involved carcass storage cleaning, stocking density, and chick delivery frequency, although the statistical support for these differences varied. Stocking density and delivery frequency reflected structural differences between systems, whereas carcass storage cleaning reflected differences in management practices. These findings suggest that interventions targeting farm-specific weaknesses, supported by tailored biosecurity plans and on-site coaching, are likely to be more effective than system-based recommendations alone.