Best practice carbon dioxide stunning for pigs

Carbon dioxide (CO2) systems stun pigs with minimal handling and physical restraint, however, they do not induce instant insensibility and pigs' aversion to CO2 has the potential to cause distress, raising animal welfare concerns. The aim of this study was to understand the factors that may influence the response of pigs to high-concentration CO2 stunning in a minimal-handling commercial abattoir and the ability to influence stunning efficacy through increased stockperson awareness of optimal animal handling. Behaviour and physiological responses of pigs as they moved from the lairage and through the CO2 stunning system were recorded utilising existing methods, prior to and post a stockperson pig handling training intervention. 

This study established a baseline for induction of loss of posture that was lower than previously reported for commercial systems, occurring less than 8 seconds after exposure to CO2, which would indicate loss of consciousness occurring by 23 seconds after first exposure. The pig handling training intervention was effective in reducing the incidence of high vocalisations and improved the flow of pigs through the raceway and stunner, reinforcing the role of the stockperson in reducing stress pre-slaughter, however, improvements in pigs' response to CO2 within modern stunning systems were not observed. The results from this study indicate that advances in design and operation of CO2 stunning systems have reduced the welfare risk to pigs compared to those reported previously, suggesting further advancements to stunning systems could be made.