Alternatives to the Use of Carbon Dioxide in Two Phases for the Stunning of Broiler Chickens at Slaughter

This study evaluated gas mixtures of carbon dioxide (CO2) associated with nitrogen (N2) as al-ternatives to the use of CO2 in two phases to improve the welfare of broiler chickens at slaugh-ter. Broilers were exposed to one of three treatments: 40C90C (1st phase: 90% CO2 and <2% O2 for 2 min, n=92), 40C60N (40% CO2, 60% N2 and <2% O2 for 4 min, n=79), or 20C80N (20% CO2, 80% N2 and <2% O2 for 4 min, n=72). The time to onset of loss of consciousness (LOC) and death was assessed by brain activity (EEG) and behaviour. Behaviour also allowed characterisation of the aversive response to the treatments. Exposure to 40C60N and 20C80N induced LOC faster (19 s [14 – 30 s] and 21 s [16 – 37 s], respectively) but also with less inter-individual variability compared to 40C90C (53 s [26 – 156 s], P < 0.001) and birds took less time to die (40C60N: 64 s [43 – 108 s]; 20C80N: 70 s [45 – 88 s]; 40C90C: 177 s [89 – 212 s], P < 0.001). The 40C90C birds not only experienced more aversion during induction to LOC but are at risk of remaining conscious when the CO2 concentration is increased in the 2nd phase. From an animal welfare point of view, 40C60N provided the highest welfare, followed by 20C80N and 40C90C.