Measures of insensibility used to determine effective stunning and killing of poultry

The ability to assess the level of unconsciousness (insensibility) in poultry is important on farms and in abattoirs, where the effectiveness of stunning and slaughter needs to be ascertained. Moreover, knowledge of the most reliable indicators of insensibility is essential to producers and researchers responsible for maintaining acceptable levels of poultry welfare. A problem with assessing insensibility in poultry is that no single method is appropriate under all circumstances, and some methods are not practical in field situations. Several measures have been recommended and used to evaluate insensibility in poultry, including brain stem reflexes, such as the corneal reflex, and spinal reflexes, such as the pain withdrawal reflex. This review examines specific advantages and disadvantages of measures that have been used to assess insensibility in studies of killing methods, and provides an overview of recommended signs of effective stunning and slaughter. The measures that are used to monitor the state of insensibility in birds during anesthesia are also examined to provide additional practical means for assessing loss of consciousness in the field. In general, the absence of brain stem and spinal reflexes provides reliable evidence of insensibility after stunning and euthanasia procedures. Although the onset of neuromuscular spasms (convulsions) does not necessarily indicate insensibility, the complete cessation of neuromuscular spasms appears to be associated with brain death. Further research is necessary to validate these measures and other indicators, such as the absence of neck muscle tension and jaw tone, as reliable indicators of complete insensibility.