Reactions of laying hens and broilers to different gases used for stunning poultry

Observations of the behavioral reactions of laying hens and broilers to different gas stunning atmospheres were made. Sixty Hy-Line W-36 hens and 60 market-weight commercial broilers were placed individually into a plexiglass gas stunning unit and exposed to one of six gas atmospheres: air, concentrations of 30, 45, or 60% CO2 in air, a mixture of 70% argon and 30% CO2, and 100% argon. Video records were made during each test, which lasted until the subject became unconscious or for 2 min in the air treatment. Behavior in the 100% argon atmosphere resembled that in air, until birds became impaired by anoxia. All treatments involving CO2, including 70% argon/30% CO2, caused deep breathing and head shaking. The concentration of CO2 in air in the range tested did not affect the tendency to perform different actions, except that birds in 60% CO2 were more likely to exhibit a convulsive flip at the point of collapse. Chickens in 70% argon/30% CO2 tended to demonstrate less sedation and performed more sudden efforts to regain balance during tests than did chickens in CO2 mixtures in air and were more likely to perform a convulsive flip. Deep breathing and head shaking have been suggested as being indicative of respiratory distress and aversive reaction to CO2. The data in this study are consistent with the possibility that head shaking is an alerting response functioning to promote arousal in the face of reduced sensibility during exposure to CO2-enriched atmospheres. Nonetheless, if the view is correct that deep breathing and head shaking indicate distress, the 70% argon/30% CO2 gas mixture was at least as distressing as even 60% CO2 in air. The relative prevalence of sudden efforts to regain balance in 70% argon/30% CO2 suggest that this gas mixture might cause even more distress than up to 60% CO2 in air.