Behavioural, brain and cardiac responses to hypobaric hypoxia in broiler chickens

Abstract

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 280 s 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 regards 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 2 s 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 50-60 s 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 49.6 s into LAPS), often associated with arrhythmia, until around 60 s 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 60 s. There were some effects of temperature A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTadjusted 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. Highlights A novel stunning system uses hypobaric hypoxia to render poultry unconscious  We measured electroencephalogram, electrocardiogram and...

Effects of ambient temperature and water vapor on chamber pressure and oxygen level during low atmospheric pressure stunning of poultry

“…One example of technology for food production is low atmospheric pressure stunning ( LAPS ) for humanely rendering chickens unconscious (Purswell et al., 2007 , Cheek and Cattaruzzi, 2009 , 2010 ). In this induced unconscious state the bird experiences no pain and discomfort during exsanguination (Vizzier-Thaxton et al., 2010 , Martin et al., 2016a , b , c ), which is a legal requirement in most countries for the slaughter of animals for food (Council Regulation (EC) No. 1099/ 2009 , OIE, 2013 ).…”

“…The LAPS process results in a non-recovery state (Mackie & McKeegan, 2016 ; Martin et al., 2016a , b , c ), a first step in preparing the birds for processing for food. However, it is difficult to quantify the levels of discomfort and pain experienced from the “stunning” procedure.…”

“…( 2016b ) using an analgesia paradigm to provide evidence that pain and discomfort levels are minimized; Martin et al. ( 2016a ) reported the effects of variation in ambient temperatures on behavioral, EEG, and ECG responses of broilers and also Martin et al. ( 2016c ) showed the effect of LAPS in both dark and light conditions and sham treatment on the behavioral, EEG, and ECG responses of broilers, demonstrating further that that LAPS is non-aversive and allows slaughter which minimizes fear, anxiety, pain, and suffering.…”

Killing for purposes other than slaughter: poultry

“…In this method, broilers are placed in containers into the decompression chamber and are exposed to gradual decompression with a reduction of available oxygen to less than 5% (Martin et al., ,b,c; Holloway and Pritchard, ). This method was found to be acceptable based on the published scientific evidence only for broiler chickens up to 4 kg live weight.…”

Slaughter of animals: poultry

“…In this method, broilers are placed in containers into the decompression chamber and exposed to gradual decompression with a reduction of available oxygen to less than 5% (Vizzier‐Thaxton et al., ; Mackie and McKeegan, 2016; Martin et al., 2016a,b,c; Holloway and Pritchard, ). This method was found to be acceptable based on the published scientific evidence for broiler chickens only up to 4 kg live weight.…”