Towards precision enrichment: tailoring housing complexity to the sensory and behavioural needs of commercial poultry

SUMMARYThe global poultry industry currently faces a critical tension between production intensification and the ethical imperative to ensure animal welfare. This comprehensive review analyzes Environmental Enrichment (EE) not merely as an aesthetic addition, but as a biological necessity defined by the modification of housing to enhance biological functioning and affective states. We critically examine the avian sensorium, highlighting how anthropocentric environments often fail the tetrachromatic vision and high Critical Flicker Fusion (CFF) frequency (~105 Hz) of poultry, potentially creating stressful stroboscopic conditions. We evaluate the disparate impacts of housing systems, identifying a bone health paradox in aviaries where increased behavioural freedom and load-bearing exercise improve bone strength yet correlate with a high prevalence of keel bone fractures due to trauma. The review further dissects the biological mechanisms underpinning enrichment efficacy, including the regulation of the Hypothalamic-Pituitary-Adrenal (HPA) axis, modulation of the gut-brain axis, and neuroplasticity derived from spatial complexity. Specific enrichment strategies are assessed for efficacy and economic viability, ranging from the use of elevated platforms to mitigate broiler leg pathologies to the implementation of dark brooders for reducing injurious feather pecking in layers. We conclude that while many enrichment interventions do not directly improve standard production metrics like weight gain, the transition towards precision enrichment tailored to specific behavioural and sensory needs is essential for mitigating physiological stress and ensuring the sustainability of the industry.