Multi-stage gas stunning of broilers in transport containers with carbon dioxide in two phases

Stunning poultry before slaughter is performed to secure animal welfare. In most slaughter houses animals are electrically stunned using a multi-bird water bath. To perform electrical stunning, animals are hung up-side down in shackles while fully conscious, which is a major animal welfare issue in the stunning process. In order to minimize animal welfare problems due to handling at removal from the transport containers, a multi-stage gas stunning system has been developed by which poultry are stunned with CO2 while in the transport containers that are placed in a closed cabinet with controlled atmosphere. Basis of this approach is induction of unconsciousness with less than 40% CO2 (Phase 1) followed by an irreversible stun using 65% CO2 (Phase 2). In both phases CO2 concentration is built up in stages to alleviate animal welfare problems and uncontrolled muscle contractions. Two different CO2 recipes were investigated with 2 different exposure times. Both recipes allowed an increase to the Phase 1 CO2 concentration (less than 40% CO2 ) within two stages. During recipe 1, the Phase 2 stunning gas concentration (65% CO2) was built up in five (5) stages with a total duration time of six (6) minutes. Recipe 2 comprised four (4) stages of one (1) minute each to reach the target Phase 2 stunning gas concentration. Slow wave EEG activity occurred at 36 ± 12seconds with recipe 1 and at 29 ± 10s with recipe 2. Suppressed EEG (loss of a and ß waves) occurred at 60 ± 23s with recipe 1 and at 50 ± 24s with recipe 2. Suppression of the EEG to approach iso-electric signal occurred at 4:07 ± 1:04 minutes with recipe 1 and at 3:27m ± 50s with recipe 2. Slow heartbeat (40% of baseline bpm) occurred shortly after exposure to increasing CO2 concentrations and prior to transitional EEG at 22 ± 13s with recipe 1 and 29 ± 27s with recipe 2. Heart failure occurs earlier with recipe 2 (4:04 ± 1:03 min.) than recipe 1 (5:54 ± 1:39 min.). No birds survived these experiments. The multi-stage gas stunning system is a consistently functioning system in which poultry can be stunned with minimal risk to animal welfare. Animals were stunned within accepted EU regulations, i.e. CO2 concentration during the induction phase remained below 40%.