Behavioural, brain and cardiac responses to hypobaric hypoxia in broiler chickens.
A novel approach to pre-slaughter stunning of chickens has been developed in which birds are rendered unconscious by progressive hypobaric hypoxia. Termed Low Atmospheric Pressure Stunning (LAPS), this approach involves application of gradual decompression lasting 280s according to a prescribed curve. We examined responses to LAPS by recording behaviour, electroencephalogram (EEG) and electrocardiogram (ECG) in individual male chickens, and interpreted these with regard to the welfare impact of the process. We also examined the effect of two temperature adjusted pressure curves on these responses. Broiler chickens were exposed to LAPS in 30 triplets (16 and 14 triplets assigned to each pressure curve). In each triplet, one bird was instrumented for recording of EEG and ECG while the behaviour of all three birds was observed. Birds showed a consistent sequence of behaviours during LAPS (ataxia, loss of posture, clonic convulsions and motionless) which were observed in all birds. Leg paddling, tonic convulsions, slow wing flapping, mandibulation, head shaking, open bill breathing, deep inhalation, jumping and vocalisation were observed in a proportion of birds. Spectral analysis of EEG responses at 2s intervals throughout LAPS revealed progressive decreases in median frequency at the same time as corresponding progressive increases in total power, followed later by decreases in total power as all birds exhibited isoelectric EEG and died. There was a very pronounced increase in total power at 50-60s into the LAPS cycle, which corresponded to dominance of the signal by high amplitude slow waves, indicating loss of consciousness. Slow wave EEG was seen early in the LAPS process, before behavioural evidence of loss of consciousness such as ataxia and loss of posture, almost certainly due to the fact that it was completely dark in the LAPS chamber. ECG recordings showed a pronounced bradycardia (starting on average 49.6s into LAPS), often associated with arrhythmia, until around 60s into LAPS when heart rate levelled off. There was a good correlation between behavioural, EEG and cardiac measures in relation to loss of consciousness which collectively provide a loss of consciousness estimate of around 60s. There were some effects of temperature adjusted pressure curves on behavioural latencies and ECG responses, but in general responses were consistent and very similar to those reported in previous research on controlled atmosphere stunning with inert gases. The results suggest that the process is humane (slaughter without avoidable fear, anxiety, pain, suffering and distress). In particular, the maintenance of slow wave EEG patterns in the early part of LAPS (while birds are still conscious) is strongly suggestive that LAPS is non-aversive, since we would expect this to be interrupted by pain or discomfort.
The Royal (Dick) School of Veterinary Studies and The Roslin Institute, Easter Bush Campus, Edinburgh, Midlothian, EH25 9RG, UK; Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, G61 1QH, UK; Animal Behaviour and Welfare, Animal and Veterinary Science Research Group, SRUC, Roslin Institute Building, Easter Bush, Edinburgh, EH25 9RG, UK. Electronic address: Jessica.Martin@ed.ac.uk.
Jessica E
JE
Martin
Centre of Excellence for Poultry Science, University of Arkansas, Fayetteville, AR 72701, United States.
Karen
K
Christensen
Centre of Excellence for Poultry Science, University of Arkansas, Fayetteville, AR 72701, United States.
Yvonne
Y
Vizzier-Thaxton
Animal Behaviour and Welfare, Animal and Veterinary Science Research Group, SRUC, Roslin Institute Building, Easter Bush, Edinburgh, EH25 9RG, UK.
Malcolm A
MA
Mitchell
Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary & Life Sciences, University of Glasgow, G61 1QH, UK.
Dorothy E F
DEF
McKeegan
D000818:Animals; D001274:Atmospheric Pressure; D001522:Behavior, Animal / Q000502:physiology*; D001921:Brain / Q000503:physiopathology*; D058256:Brain Waves / Q000502:physiology*; D002645:Chickens / Q000502:physiology; D004562:Electrocardiography; D004569:Electroencephalography; D006339:Heart Rate / Q000502:physiology*; D000860:Hypoxia / Q000473:pathology* / Q000503:physiopathology*; D016014:Linear Models; D008297:Male; D011930:Reaction Time / Q000502:physiology
Animal welfare; Behaviour; Electrocardiogram; Electroencephalogram; Hypobaric hypoxia; Low atmosphere pressure stunning