A study conducted by researchers in Scotland and the Netherlands suggests that a new form of poultry stunning does not cause the bird's distress when rendering birds unconscious prior to slaughter. The results of the study appear in Poultry Science, a journal published by the Poultry Science Association. The article entitled "Physiological Responses to Low Atmospheric Stunning and the Implications for Welfare" is available for download at the Poultry Science website.

Low atmospheric pressure stunning

The paper's lead author, Dr. Dorothy McKeegan of the Institute of Biodiversity, Animal Health and Comparative Medicine at the University of Glasgow, spoke about some of the factors behind her team's research on a new approach, called low atmospheric pressure stunning.

"Electrical stunning remains the world's most widely used method of rendering poultry unconscious prior to slaughter. But concerns about stress caused to poultry by shackling prior to electric stunning and variability in its effectiveness have led to legislation that will reduce the use of this approach in Europe and to the investigation of other approaches that may be less stressful to the bird. In our research, we found that low atmospheric pressure stunning has the potential to improve the welfare of poultry at slaughter by gradually inducing unconsciousness without distress, eliminating the stress of shackling and ensuring that every bird is adequately stunned prior to exsanguinations," McKeegan said.

In low atmospheric pressure stunning, poultry are rendered unconscious just prior to slaughter by gradually reducing oxygen tension in the atmosphere. The study address whether there were any indicators of distress to the birds by collecting and analyzing physiological data during the low atmospheric pressure stunning process.

Summary of study and findings

To determine whether the stunning process is stressful, the authors outfitted 28 broiler chickens with wireless, self-contained telemetry logging units to capture high-quality, continuous electroencephalogram and electrocardiogram data. The data recordings were obtained in a commercial poultry processing plant, which is currently using low atmospheric pressure stunning.

The researchers found that it took 40 seconds for the chicken to lose consciousness after the stunning process began. During this period they noted an increase in slow-wave, or delta wave, brain activity, consistent with a gradual loss of consciousness. The increase in delta wave activity began within 10 seconds after the initial stun and continued thereafter. Delta wave activity peaked at 30 seconds into the process, at which point it was consistent with the electroencephalogram signals of birds under surgical levels of anesthesia.

The researchers also found that, during the application of low atmospheric pressure stunning, the birds' heart rates consistently decreased. They found no instances in which heart rates increased during the period when the birds were potentially conscious. They also observed no behavioral responses that would suggest aversion to the low atmospheric pressure stunning process.

The authors concluded that "the scientific data strongly suggest that birds do not find low atmospheric pressure stunning induction distressing," and that "collectively, the results indicate that low atmospheric pressure stunning is an effective and humane alternative approach to stunning prior to slaughter."