Carbon dioxide stunning is used for stunning pigs in many countries. There have been welfare concerns about CO2 because it is a pungent gas which is irritating to the respiratory tract (Gregory, 1994). One research lab reports that CO2 is aversive to pigs (Raj et al, 1999). Another research team states that it is not aversive (Jong et al, 2000).
Stress caused by forcing pigs to move through a single file race could be eliminated by stunning groups of pigs in CO2 gas. Barton Gade et al. (1993) has developed a low stress driving and lairage system for moving groups of five pigs onto an elevator which descends into CO2 gas. An entire system approach should be used for evaluating CO2 stunning. Some discomfort during the induction of anesthesia may be a small price to pay for great reductions in handling stress, but if the pigs violently attempt to escape when they first inhale the gas, this is not acceptable. The group handling systems that are now available really improve pig handling. These systems make it possible to totally eliminate electric prod use to move pigs into the CO2 chamber because the single file race is now eliminated. When new CO2 systems are installed, it is strongly recommended to purchase group systems, where a group of pigs are moved from a small pen into an elevator (gondola) which lowers them into the CO2.
Effect of genetics on handling and CO2 stunning of pigs (with July 2008 updates)
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