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

Abstract

1. The effects of controlled atmosphere stunning on behavioural and physiological responses, and carcase 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 for CO₂ + O₂ birds whereas it declined gently for Ar + CO₂ birds.

5. In terms of carcase and meat quality, there appeared to be clear advantages to the processor in using CO₂ + O₂ rather than Ar + CO₂ to stun broiler chickens, for example, a much smaller number of fractured wings (1·6 vs. 6·8%) with fewer haemorrhages of the fillet.

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 carcase and meat quality, over a single phase hypercapnic anoxic approach employing 60% Ar and 30% CO₂ in air with <2% O₂.

Acknowledgements

The behavioural and physiological aspects of this work were funded by the Department for Environment, Food and Rural Affairs, UK, while those relating to meat and carcase quality and the use of the processing plant were funded by Stork PMT and Yara International ASA.