Effects of analgesic intervention on behavioural responses to Low Atmospheric Pressure Stunning

Worldwide, more than 50 billion chickens are killed annually for food production so their welfare at slaughter is an important concern. Low Atmospheric Pressure Stunning (LAPS) is a novel approach to pre-slaughter stunning of poultry in which birds are rendered unconscious by gradually reducing oxygen tension in the atmosphere to achieve a progressive anoxia (hypobaric hypoxia). Advantages of this approach over electrical stunning are that birds are not shackled while conscious and all birds are reliably and irreversibly stunned. However, concerns remain that birds undergoing LAPS could experience discomfort or pain. Here we investigated whether subjecting birds to LAPS with and without administration of an opioid analgesic (butorphanol) affected behavioural responses. A blocking design was used in which pairs of birds receiving either analgesic or sham treatment were allocated to three types (analgesic/analgesic, analgesic/sham, or sham/sham). In line with previous studies, birds showed a consistent sequence of behaviours during LAPS: ataxia, loss of posture, clonic/tonic convulsions, leg paddling and motionless. Overall, administration of butorphanol had no effect on the range and patterning of behavioural responses during LAPS, but there were some differences in behaviour latencies, counts and durations. For example, latencies to ataxia, mandibulation and deep inhalation were delayed by analgesic treatment, however the duration of ataxia and other behaviours related to loss of consciousness were unaffected. Fewer birds receiving analgesia showed jumping and slow wing flapping behaviour compared to controls, which suggests these may be pain related. These behaviours after the onset of ataxia and the results may reflect a smoother induction to unconsciousness in analgised birds. Collectively, the results do not provide convincing evidence that birds undergoing LAPS are experiencing pain. While there were effects of analgesia on some aspects of behaviour, these could be explained by potential sedative, dysphoric and physiological side effects of butorphanol. The behavioural responses to LAPS appear to be primarily related to exposure to anoxia rather than hypobaric conditions, and thus in terms of welfare, this stunning method may be equivalent to controlled atmosphere stunning with inert gases