Carbon dioxide stunning causes aversion and distress in pigs before unconsciousness. Research into alternatives represents a major welfare priority.
Pigs stunned with CO2 experience distress for 20-30 seconds before losing consciousness - a significant welfare deficit affecting hundreds of millions of animals annually. The aversive nature of CO2 is not a necessary feature of stunning but a result of economic factors. Research and investment in alternative systems represents one of the most impactful welfare improvements possible.