Multistage carbon dioxide gas stunning of broilers

The stunning quality of animals for slaughter remains under constant scrutiny. In response to previous research showing low stunning efficiency in poultry, the conventional water bath will be phased out in the Netherlands. Presently, the main practical alternative to water bath stunning of poultry is a 2-phased gas stunning method. Gas stunning methods are recognized by governments and animal welfare organizations across Europe. In this study, 3 sets of experiments were conducted on gas stunning methods using CO2 in 2 phases. Two methods were examined to identify potential effects on bird behavior and investigate their practical implications: a 5-stage incremental CO2 scheme lasting 6 min (treatment 1) and a 4-stage incremental CO2 scheme lasting 4 min (treatment 2). The onset and duration of unconsciousness were specifically tested in experiment 2 by using 25 birds equipped with electrodes monitoring brain and heart activity. Behavioral responses were observed on 15 non-instrument-monitored birds kept in the same cages at that time. Results in all 3 sets of the experiments showed that multistage gas stunning was stable and consistent, and increases in CO2 concentrations were rapid and reliable. Ambient temperatures and RH of the air remained within acceptable levels at all times. Induction of unconsciousness occurred below 40% CO2 and did not significantly differ between treatments. Conscious birds were never exposed to high CO2 concentrations (>40% CO2), yet some birds showed signs of distress (e.g., head shaking, wing flapping) before losing consciousness. Discomfort experienced during exposure to low