Controlled atmosphere stunning of broiler chickens. II. Effects on behaviour, physiology and meat quality in a commercial processing plant

International audienceABSTRACT 1. The effects of controlled atmosphere stunning on behavioural and physiological responses, and carcass and meat quality of broiler chickens were studied experimentally in a full scale processing plant. 2. The gas mixtures tested were a single phase hypercapnic anoxic mixture of 60% Ar and 30% CO2 in air with <2% O2, and a biphasic hypercapnic hyperoxygenation mixture, comprising an anaesthetic phase, 40% CO2, 30% O2, 30% N2, followed by an euthanasia phase: 80% CO2, 5% O2, 15% N2. 3. Birds stunned with Ar+CO2 were more often observed to flap their wings earlier, jump, paddle their legs, twitch, and lie dorsally (rather than ventrally) than those stunned with CO2+O2. These behaviours indicate a more agitated response with more severe convulsions during hypercapnic anoxia, thereby introducing greater potential for injury. 4. Heart rate during the first 100 s of gas stunning was similar for both gases, after which it remained constant at ≈ 230 beats min-1 for CO2+O2 birds whereas it declined gently for Ar+CO2 birds. 5. In terms of carcass and meat quality there appeared to be clear advantages to the processor in using CO2+O2 rather than Ar+CO2 to stun broiler chickens, e.g. a much smaller number of fractured wings (1.6 vs. 6.8 %) with fewer haemorrhages of the fillet. Meat quality was similar in both gas mixtures. 6. This study supports the conclusions of both laboratory and pilot scale experiments that controlled atmosphere stunning of broiler chickens based upon a biphasic hypercapnic hyperoxygenation approach has advantages in terms of welfare and carcass quality over a single phase hypercapnic anoxic approach employing 60% Ar and 30% CO2 in air with <2% O2