Broiler chickens — birds bred specifically for rapid meat production — represent the largest number of farmed land animals globally. Approximately 70 billion broilers are produced annually. Their welfare is influenced by genetic selection, housing systems, management practices, and slaughter conditions.
Modern broiler genetics have produced birds that reach slaughter weight (2.2–2.5kg) in 35–38 days. This extraordinary growth rate — driven by selection for feed conversion efficiency and breast muscle yield — has created a range of health problems inherent to the genotype. Key welfare concerns from genetics include: leg weakness and lameness from disproportionate muscle mass relative to skeletal development, ascites (fluid accumulation in the abdomen) from cardiac and pulmonary systems unable to support rapid growth, sudden death syndrome (SDS), and contact dermatitis from prolonged lying on litter.
Slower-growing breeds (slower than 45g/day weight gain) are promoted by welfare organisations as a solution — the European Chicken Commitment requires use of breeds below specific growth thresholds. Slower-growing birds have significantly lower leg disorder prevalence and mortality but require longer production periods and more feed.
The majority of global broiler production uses intensive indoor systems on litter (straw, wood shavings, or rice husks). EU Directive 2007/43/EC sets minimum stocking densities at 33kg/m² (up to 42kg/m² with derogation). RSPCA Assured requires a maximum 30kg/m² and additional enrichment. Higher stocking densities increase contact dermatitis (hock burns and breast lesions), reduce mobility, impair air quality (higher ammonia), and reduce per-bird space for all activities.
Enrichment provisions including perches, straw bales, pecking objects, and natural light cycles improve welfare by providing environmental complexity, opportunities for natural behaviours, and more appropriate light rhythms. The barren, high-density shed is the worst welfare outcome; well-managed enriched housing with lower density and natural light is substantially better.
Lameness: Gait scoring (0–5 scale) assesses locomotion. Welfare surveys find 25–35% of conventional production birds with significant lameness (score 3+). Lameness causes pain and reduced access to feed and water.
Hock burns: Skin lesions on the hocks from contact with wet, contaminated litter. Prevalence reflects litter management quality. High prevalence indicates poor welfare conditions.
Mortality: On-farm mortality above 4% suggests systemic welfare problems. Culling of poor-doing birds (blow culling) must be performed humanely.
Catching for transport is a significant welfare event. Traditional manual catching (grabbing birds by the legs) causes bruising and stress. Mechanical catching reduces injury rates but requires careful equipment maintenance and operator training. Transport density, journey duration, and temperature management all affect welfare. Pre-slaughter holding at lairage should be minimised.
Controlled atmosphere stunning (CAS) using nitrogen or CO₂ kills birds with unconsciousness before hanging, eliminating the live shackling welfare problem. Water bath stunning (live shackling before electrical stun) remains common and raises significant pre-stun welfare concerns. All slaughter systems require effective stunning validation and back-up procedures for failed stuns.
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