Behavioural responses during exposure of broiler chickens to different gas mixtures

Abstract

An alternative stunning system to the generally applied electrical water bath stunner for broiler chickens is gas stunning. This method of stunning can eliminate the stress associated with uncrating and/or shackling of live birds prior to electrical stunning. Behavioural responses to inhalation of gas were examined during exposure of broilers to different gas mixtures. In total, 137 six-week-old broiler chickens were individually immersed in a gas chamber containing one of the following gas mixtures: (a) 90% Ar/air, (b) 30% CO 2/60% Ar/air or (c) 40% CO 2/30% O 2/30% N 2. The birds moved freely or were restrained. Behavioural parameters were recorded on video and analysed for gasping, headshaking, wing flapping and loss of posture. The number of gasps before loss of posture declined progressively on exposure to gas mixtures Ar/air or Ar/CO 2/air or CO 2/O 2/N 2, respectively, and remained high after loss of posture in the latter gas mixture. Gasping occurred rarely in broilers during exposure to gas mixture Ar/air. When gas mixture CO 2/O 2/N 2 was used the loss of posture was significantly delayed compared to the gas mixture Ar/air and Ar/CO 2/air. The number of headshakes and wing flapping was significantly higher in the restrained groups of birds compared to the free moving group. Wing flapping was low before and after loss of posture in gas mixture CO 2/O 2/N 2. It is concluded that during the immersion in gas mixtures broilers show gasps, head shakes and wing flapping which start before loss of posture, which may cause some distress. However, it can be argued that gas stunning compared to water bath stunning is preferred in practical applications, because the live broilers do not need to be uncrated and/or shackled.