Pre-slaughter stunning ensures pigs are unconscious before bleeding. Different methods vary significantly in welfare outcomes and industry adoption.
The 30-60 seconds pigs spend in high-concentration CO2 involves clear distress signals - frantic activity, vocalisation, hyperventilation - indicating aversive experience before unconsciousness. Inert gas systems that induce anoxia via nitrogen or argon show markedly less aversion and are increasingly adopted in welfare-progressive facilities. Transitioning from CO2 to inert gas stunning represents one of the single highest-impact welfare improvements available to the pig industry given the enormous numbers of pigs slaughtered annually.