Controlled atmosphere stunning using high CO2 or low oxygen gas mixtures is increasingly used in poultry slaughter, with significant welfare differences between different gas compositions and concentrations.
Poultry entering high-CO2 chambers experience the aversive sensation of CO2 exposure for 15-30 seconds before losing consciousness. Chickens show wing flapping, escape attempts and distress vocalisation during CO2 exposure. Low-oxygen systems using inert gases achieve unconsciousness without the aversive sensory experience of CO2. The welfare difference between systems is significant for the hundreds of millions of birds slaughtered annually.