Controlled Atmosphere Stunning

Abstract

Controlled atmosphere (CAS) stunning includes several variations of gaseous mixtures given to induce an anaesthetic state before slaughter poultry. One method of multi phase CAS is to unload the birds out of the crate on a conveyor belt and subject the birds to an atmosphere of 30% O2, 40% CO2 and 30% N2 for 1 min to stun them followed by an atmosphere of 80% CO2 and 5% O2 for 2 min. Another approach of CAS involves exposure of poultry while remaining in the crates in a chamber to a mixture of inert gasses to produce anoxic loss of consciousness. This approach includes killing with a number of different gasses by anoxia such as Ar and N2 content up to 90% with a CO2 content limited to 30% and O2 maximised by 2%. Initially Ar and O2 were used in contents of > 90% and 2%, respectively. At present N2 and Ar with/ or without CO2 for broilers and N2 with CO2 are used for turkey. After stunning the birds are shackled, exsanguinated and slaughtered. CO2 is an naesthetic gas which produces rapid unconsciousness when inhaled at high concentrations, however, signs of asphyxia and behavioural excitation are observed due to occurrence of both hypercapnia and hypoxia. More over, it is an acidic gas. It is likely that an avoidance response is mediated by the olfactory system in birds. Exposure of birds to 90% Ar in air or 60% Ar / 30% CO2 in air results in an anoxic condition. Anoxia results in suppression of the rostral reticular formation and therefore loss of consciousness and in suppression of the caudal reticular formation and therefore onset of convulsions. Wing flapping is observed before the onset of loss of posture when exposed to Ar or Ar / CO2 gas mixtures