Review: Potential alternatives to high-concentration carbon dioxide stunning of pigs at slaughter.

Using carbon dioxide (CO) for stunning pigs at slaughter is common in Europe. The use of group stunning is a major advantage with CO, which is done without restraining the pigs and with minimized human contact. However, high concentrations of CO have been known for decades to cause pain, fear and distress in pigs before loss of consciousness, and the stunning method is clearly associated with animal welfare concerns. This study reviewed the scientific literature to find recent developments or evaluations of alternative methods that could lead to the replacement of CO for stunning pigs at slaughter. Potential alternative methods found in the literature were described and then assessed to identify specific research and development needs for their further development. Only 15 empirical studies were found in the search of peer-reviewed literature since 2004, which is less than one per year. Furthermore, half of the studies focused on evaluating methods to improve high-concentration CO stunning rather than an alternative to CO. Since no clear alternative has emerged, nor a method to improve CO stunning, there is obviously a strong need to focus research and development to find solutions for improving animal welfare when stunning pigs at slaughter.