Muscle spasms during pre-slaughter CO2-anaesthesia in pigs

Six exposures to 95 % CO2 for one minute were made in four pigs. Following onset of CO2-inhalation muscle jerks were observed after a latency of about 15 s. At this time the EEG showed a slow wave pattern typical of general anaesthesia. The short latency muscle jerks were by all probability no emotional stress reactions, but instead the motoric manifestation of a release phenomenon. Therefore, it is concluded that the occurrence of muscle jerks does not invalidate the ethics of preslaughter CO2-anaesthesia in swine.