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Abstract
A requirement under humane slaughter regulation is that stunning methods should induce immediate loss of consciousness and sensibility. If the onset of unconsciousness is not immediate, the induction of unconsciousness with a stunning method should not cause in animals avoidable anxiety, fear, pain, distress or suffering. The duration of unconsciousness induced by a stunning procedure must be longer than the sum of time that lapses between the end of stun and the time to onset of death. Since the effect of a stunning method is momentary, the onus of preventing resumption of consciousness thereafter relies on the efficiency of slaughter procedure; i.e. the prompt and accurate severance of blood vessels supplying oxygenated blood to the brain. Electrical water baths and gas or controlled atmospheres are commonly used for stunning poultry under commercial conditions. The electrical waveforms (sine wave alternating current or pulsed direct current) and frequencies (Hz) employed to stun poultry and the amount of current applied to individual birds in a water bath stunner widely varies. Rationalisation of electrical variables is urgently warranted. Varieties of gas mixtures have been proposed or used for stunning or killing poultry in crates or conveyors however the bird welfare implications have not been communicated effectively to facilitate progress.
This review deals with the efficacy of electrical variables used in the water baths and of slaughter methods, and the relative merits of different gas mixtures used for stunning or killing broilers.