Controlled Atmosphere Killing for Poultry: Welfare Evidence and Industry Adoption

Controlled atmosphere killing (CAK) using high concentrations of carbon dioxide or inert gases is increasingly proposed as a more welfare-positive alternative to electrical water-bath stunning for poultry slaughter.

Key Facts

Conventional electrical water-bath stunning for poultry requires live birds to be shackled upside down and dragged through electrified water — causing fear, pain from wing flapping, and pre-stun shocks in a proportion of birds
Controlled atmosphere killing uses gas mixtures — typically high CO2, or inert gases such as argon and nitrogen — to render birds unconscious before they are shackled or handled further
High CO2 concentrations (above 30%) cause aversion and distress in birds before unconsciousness; lower CO2 mixed with inert gases (argon or nitrogen) causes unconsciousness more rapidly and with less apparent distress
Multi-phase systems that gradually increase CO2 are considered more aversive than single-phase high CO2 or inert gas systems
CAK eliminates pre-stun electric shocks and the trauma of shackling conscious birds — the two primary acute welfare concerns in conventional water-bath systems
The EFSA Scientific Panel on Animal Health concluded that inert gas CAK systems are among the best available methods for commercial poultry slaughter welfare
CAK adoption remains uneven globally: common in some UK and Scandinavian operations but less prevalent in the US, where water-bath stunning remains dominant

Welfare Considerations

The welfare case for replacing water-bath electrical stunning with well-designed CAK systems is strong for commercial broiler slaughter. The suffering associated with shackling conscious birds — particularly the fear response, wing injury risk, and pre-stun shocks affecting a documented proportion of birds — is eliminated. The key welfare variable in CAK is gas composition: high CO2 alone causes aversion and distress, while inert gas or low-CO2 systems with rapid loss of consciousness are significantly better. At the scale of commercial poultry production — billions of birds globally — even small improvements in the slaughter process translate into enormous reductions in aggregate suffering.

What You Can Do

Support poultry welfare certification schemes that require or incentivise CAK with low-aversion gas mixtures
Ask supermarkets and food service companies about their poultry supplier slaughter method standards
Advocate for regulatory reform requiring inert gas or low-CO2 CAK as the minimum standard for commercial poultry slaughter
Support research into CAK system design that minimises aversion while maintaining operational efficiency
Reduce poultry consumption or shift to higher-welfare certified products as consumer pressure for better slaughter practices
Back food company shareholder resolutions requiring supply chain slaughter welfare disclosure and improvement
Engage with the Open Wing Alliance and Humane Slaughter Association on poultry slaughter welfare campaigns