Low atmospheric pressure stunning (LAPS) is a new irreversible stunning method for broiler chickens (Gallus gallus domesticus), which has the potential to improve welfare during routine slaughter. During LAPS, birds are placed in a hypobaric chamber that allows oxygen to be gradually removed from the environment by the controlled removal of air; the staged process takes 280s and reaches final decompression pressure that is 80.6 kPa below atmospheric pressure (nominally 101.3 kPa for an absolute vacuum pressure of 20.7 kPa). In this study, the behaviour of broilers (50 individuals and 50 focal birds killed in groups of 20) was observed during LAPS. Latencies, total durations, single bout durations and number of bouts were recorded for all behaviours. Three different decompression curves were applied during the process (based on automatically applied settings related to ambient temperature) and their effects on behaviour were investigated. Not all birds displayed all behaviours, but a subset of behaviours (ataxia, loss of posture, clonic and tonic convulsions and leg paddling) occurred in a consistent sequence. In individuals, mandibulation, headshaking and open bill breathing occurred earliest at 44.5 ± 31.6 s, 50.8 ± 38.3 s and 57.4 ± 35.8 s, respectively, after LAPS began. Ataxia was observed on average at 57.3 ± 11.5 s, with birds killed at colder temperatures taking slightly longer to succumb to ataxia than those at warmer temperatures. Loss of posture (LOP) is regarded as a behavioural marker for loss of consciousness and it occurred on average at 80.7 ± 17.7 s. Clonic and tonic convulsions were displayed after LOP at 110.5 ± 37.6 s and 117.4 ± 28.8 s after LAPS onset, respectively. Mean time to motionless was 199.4 ± 21.3 s. The group data were largely similar to that of individuals but were less reliable due to focal birds being obscured by neighbours. Based on LOP, the data suggest that birds are in a conscious state for longer during LAPS than in controlled atmosphere stunning with inert gases, but although the induction to unconsciousness is more gradual, other behavioural responses were equivalent. The occurrence of mandibulation, head shaking, and open bill breathing may be an indication of reduced welfare or may be indications of a non-painful physiological responses to hypoxia in a hypobaric atmosphere. These behaviours occurred at similar levels as seen in CAS with inert gases in poultry and the lack of escape behaviours as well as absence of signs of severe dyspnoea suggest that LAPS is a humane approach to stunning of poultry.
- Animal welfare
- Hypobaric hypoxia
- Humane slaughter
- Loss of posture
- Low atmosphere pressure stunning