Review: Pig welfare around slaughter and impacts on carcass and meat quality.

Pig welfare around slaughter remains a sensitive issue, as animals are exposed to multiple hazards within a short period. The objective of this review was to provide a comprehensive assessment of the key factors affecting pig welfare in commercial slaughterhouses, to evaluate their impact on meat quality, and to examine contemporary alternatives to high-concentration CO2 stunning with respect to their implications for both animal welfare and meat quality. During lairage, exposure to a novel environment and unfamiliar animals can hinder recovery from transport stress. Limited space allowance negatively impacts welfare by impairing rest, exacerbating heat stress, and increasing agonistic behaviours. Cooling strategies, such as intermittent water spraying, can improve thermal comfort and reduce stress within groups. Although feed withdrawal is necessary for food safety, it should be limited to less than 16 h to avoid prolonged hunger and additional stress. Handling practices during movement to the stunning point are another significant source of stress when poorly executed. Effective stunning is essential to ensure that pigs are rendered unconscious without pain before exsanguination. While electroencephalography remains the most accurate method to assess consciousness, practical evaluation in commercial settings relies on animal- and resource-based indicators, whose reliability depends on standardised protocols and proper training. The two most widely used stunning methods are electrical stunning and exposure to high concentrations of CO2. Electrical stunning induces immediate unconsciousness but raises welfare concerns due to handling and restraint, particularly in high-throughput systems. In addition, the use of electric goads to move pigs from groups into raceways, although reducible, cannot yet be eliminated, highlighting the need for improved facility design. CO2 stunning, although widely adopted, is aversive, as it induces hyperventilation and irritation of mucous membranes. Alternatives such as improved electrical systems and inert gas stunning using argon, nitrogen, or helium at residual oxygen levels below 2% show potential welfare benefits by reducing pain, fear, and respiratory distress. However, these systems typically result in slower induction of unconsciousness and faster recovery, posing practical challenges. Preslaughter stress significantly affects carcass and meat quality, leading to defects such as bruising, blood spots, and alterations in colour, firmness, and water-holding capacity. In severe cases, this results in conditions such as pale, soft, and exudative or dark, firm, and dry pork, reducing product quality and economic value. Implementing low-stress handling and optimised stunning practices can improve both animal welfare and meat quality outcomes.