In response to recent comments made by the Association of Independent Meat Suppliers (AIMS) which described carbon dioxide (CO₂) stunning as “delivering exceptional welfare outcomes,” Compassion in World Farming strongly disagrees with this characterisation.

While it is true that pigs in CO₂ stunning systems are often moved calmly in small social groups, which can reduce pre-stun handling stress and fear, this does not mitigate the severe welfare concerns associated with the use of high concentrations of CO₂

Scientific evidence shows that CO₂ causes significant suffering in pigs

For decades, scientific evidence has consistently shown that CO₂ stunning causes significant suffering. The European Food Safety Authority (EFSA) has reiterated that exposure to CO₂ concentrations above 80% results in pain, fear, and respiratory distress, making it a serious welfare concern. Pigs subjected to CO₂ stunning experience severe pain in their eyes, nose, mouth, and lungs, along with panic, anxiety, gasping, and respiratory distress for 21 to 60 seconds before losing consciousness.

To be considered humane, stunning methods must either be non-aversive or cause instantaneous loss of consciousness which lasts until death supervenes. CO₂ stunning is both aversive and not instantaneous.

Findings from the PigStun project

The recently concluded EU-coordinated PigStun project has provided compelling evidence for alternative methods that significantly improve welfare. These include an enhanced electrical stunning system and an argon gas system. The electrical stunning system involves improved walkway design and handling of pigs, significantly reducing pre-stunning stress. Electrical stunning then induces near-instantaneous unconsciousness, meaning the pigs do not experience pain. Although argon gas stunning takes slightly longer than CO₂, it does not cause pain or respiratory distress, resulting in calmer pigs and improved welfare.

As the PigStun project concluded:
“The tested systems pose the opportunity to significantly increase animal welfare for pigs at slaughterhouses, and slaughterhouses should consider the possibility of changing to one of them.”

Compassion urges the industry to move away from CO₂ stunning and adopt more humane alternatives that align with both scientific evidence and ethical responsibility.

Our response to AIMS' statement on CO₂ stunning for pigs