Prior to slaughter, most farmed birds move through a constant-voltage, multiple- bird, electrical water-bath stun system. Using this system subjects live birds to stressful and painful shackling, and the potential exists for them to receive prestun electric shocks and induction of seizures while still conscious. The existing elec- trical water-bath stunner settings, particularly those used in U.S. slaughter plants, are not necessarily based on sound scientific data that they produce a consistent, immediate stun, and research indicates that they are not effective in all birds. Further, in multiple-bird, electrical water-bath systems, birds may miss the stunner completely. Evidence suggests that some birds may still be alive when they reach the scald vat. For these reasons, electrical water-bath systems are increasingly under scrutiny on nonhuman-animal welfare grounds. Controlled Atmosphere Killing (CAK), a promising alternative technology, uses gas mixtures to render birds unconscious. CAK systems that stun birds while they are still in their transport crates avoid many of the welfare problems associated with the live-hang process and electrical water-bath stunning.
Shields, S. J., & Raj, A. B. M. (2010). A critical review of electrical water-bath stun systems for poultry slaughter and recent developments in alternative technologies. Journal of Applied Animal Welfare Science, 13(4), 281-299.