Welfare implications of low atmospheric pressure stunning (LAPS)

In low atmospheric pressure stunning (LAPS), poultry are rendered unconscious prior to slaughter by gradually reducing oxygen tension in the atmosphere to achieve a progressive anoxia. The effects of LAPS are not instantaneous so there are legitimate welfare concerns around the experience of birds prior to loss of consciousness. Using self contained telemetry logging units, high quality continuous electroencephalogram (EEG) and electrocardiogram (EKG) recordings were obtained from 28 broiler chickens during exposure to LAPS in a commercial poultry processing plant. Application of LAPS was associated with changes in the EEG pattern in the form of increases in total power (PTOT), decreases in mean frequency (F50) and in particular, increases in slow wave (delta) activity,
indicating a gradual loss of consciousness. Increased delta wave activity was seen within 10s of LAPS onset and consistently thereafter, peaking at 30s into LAPS at which point the EEG signal shared characteristics with that of birds in a surgical plane of anaesthesia. During LAPS, heart rate consistently decreased, with more pronounced bradycardia and arrhythmia observed after 30s. No heart rate increases were observed in the period when the birds were potentially conscious. After an initial quiescent period, brief body movements (presumed to be ataxia/loss of posture) were seen on average at 39s into the LAPS process. Later (after 120s on average), artifacts related to clonic (wing flapping) and tonic (muscle spasms) convulsions were observed in the EKG recordings. Based on
EEG analysis and body movement responses, a conservative estimate of time to loss of consciousness is approximately 40s. The lack of behavioral responses indicating aversion or escape and absence of heart rate elevation in the conscious period strongly suggest that birds do not find LAPS induction distressing. Collectively, the results suggest that LAPS is a humane approach which has the potential to improve the welfare of poultry at slaughter by gradually inducing unconsciousness without distress, eliminating live shackling and ensuring every bird is adequately stunned before exsanguination.