Investigation into the batch stunning/killing of chickens using carbon dioxide or argon-induced hypoxia

Three hundred and twenty broilers were stunned for 2 minutes in batches of 10 per crate in four treatments: 45 per cent carbon dioxide; 55 per cent carbon dioxide; 2 per cent oxygen, or 5 per cent oxygen presented as air diluted by argon. The number of survivors and the time to resumption of consciousness were recorded using the time to eye opening and response to comb pinching as indicators of consciousness. In 45 per cent and 55 per cent carbon dioxide and 2 per cent oxygen, 28, none and eight birds, respectively, survived out of 100 in each group. In 5 per cent oxygen the birds were still fully conscious after a 2 minute exposure period, and the test was discontinued. The time to recovery could be rapid after stunning in both the gases. It is suggested that a concentration of 55 per cent carbon dioxide or less than 1 per cent oxygen are required to kill broilers within a 2 minute exposure period, and that care should be taken to ensure that there is sufficient turbulence within the stunning chamber to avoid air pockets being trapped between the birds.