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 recognised by governments and animal welfare organisations across Europe. In this study, 3 sets of experiments were conducted on gas stunning methods using CO(2) in 2 phases. Two methods were examined to identify potential effects on bird behavior and investigate their practical implications: a 5-stage incremental CO(2) scheme lasting 6 min (treatment 1) and a 4-stage incremental CO(2) 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 CO(2) concentrations were rapid and reliable. Ambient temperatures and relative humidity of the air remained within acceptable levels at all times. Induction of unconsciousness occurred below 40 per cent CO(2) and did not significantly differ between treatments. Conscious birds were never exposed to high CO(2) concentrations (>40 per cent CO(2)), yet some birds showed signs of distress (eg head shaking, wing flapping) before losing consciousness. Discomfort experienced during exposure to low (<40 per cent) CO(2) concentrations compares favorably with the experiences of handling, tilting, and or shackling of conscious birds when using alternative stunning methods, implying that multistage gas stunning has distinct advantages for bird welfare. Compared with the multibird water bath system, this method provides an opportunity to guarantee that all birds are properly stunned. The risk of convulsions, which was higher with treatment 2, leading to possible injuries, indicates a preference for the 5-stage treatment. The study is from Wageningen UR Livestock Research, Lelystad, the Netherlands.
Gerritzen MA, Reimert HG, Hindle VA, et al. Poult Sci 2013; 92(1): 41-50.