The objective of this review was to summarize the currently available data describing the sensitivity and specificity of indicators of unconsciousness and death in the following stun-kill methods and species combinations:
1) Penetrative captive bolt for bovine animals
2) Head-only electrical stunning for pigs
3) Head-only electrical stunning for sheep and goats
4) Electrical waterbath for poultry (chickens and turkeys)
5) Carbon dioxide at high concentration for pigs
6) All authorized gas methods to slaughter chickens and turkeys (carbon dioxide at high concentration, carbon dioxide in two phases, carbon dioxide associated with inert gases and inert gases alone)
7) Slaughter without stunning for bovine animals
8) Slaughter without stunning for sheep and goats
9) Slaughter without stunning for chickens and turkeys
The reference tests for unconsciousness and death were to have been measured using electroencephalography (EEG). The definition of unconsciousness and death based on EEG were not specified, and the definition used by authors was reported. The index tests of interest were a variety of indicators requested by the funding agency such as no corneal reflex and immediate collapse.
The index tests differed by stun-kill methods and species combination. A comprehensive search identified 22 publications contained 24 species-stun/kill method combinations.
No studies explicitly reported the sensitivity and specificity of the indicators in conscious and unconscious animals. Many studies reported the proportion of stunned animals with indicators, rather than the proportion of unconscious or conscious animals at a set time point with the indicators. Such data could not be translated into sensitivity and specificity.
Other studies reported the average time to occurrence of an indicator or average time to cessation of the indicators. Such data cannot be translated into sensitivity and specificity estimates without knowledge of the joint distributions.