What are the animal welfare issues with carbon dioxide stunning?
Commercial carbon dioxide stunning involves pigs being exposed to high concentrations (greater than 80% by volume in air) of carbon dioxide resulting in gradual loss of consciousness. Recent studies have revealed a number of welfare issues with high concentration of carbon dioxide stunning:
- concentrations greater than 30% are highly aversive (very unpleasant, painful) for pigs
- there is variability between pigs' responses to carbon dioxide
- pigs are not rendered unconscious immediately
- high concentrations of carbon dioxide gas can cause significant pain and distress to pigs when inhaled due to acute respiratory distress
Studies of pigs' behavior have found that most pigs will avoid high concentrations of carbon dioxide if possible and that almost 90% of pigs prefer to go without water for 72 hours rather than experience exposure to carbon dioxide gas.