The impact of stockperson training on time to loss of posture in a minimal-handling high-concentration carbon dioxide stunning system

Abstract

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 s after exposure to CO₂, which would indicate loss of consciousness occurring by 23 s 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.