Electroencephalographic studies of stunning and slaughter of sheep and calves-part 2: The onset of permanent insensibility in calves during slaughter.

The time of onset of permanent insensibility, subsequent to incision of the major blood vessels of the neck, was studied in eight one-week-old calves. Insensibility was determined from the study of electroencephalograms (EEG). Apart from one animal in which insensibility first occurred within 34 s, the first indication of insensibility did not occur until between 65 and 85 s. All animals subsequently showed evidence of periodic resurgence of possible sensibility for up to 123 to 323s after slaughter. Such resurgences were seen to be preceded by a respiratory gasp. The EEG did not become isoelectric until between 132 and 336 s. Involuntary movements of the animal and the presence of corneal and palpebral reflexes persisted for up to 300 s after slaughter. It is suggested that the marked increase in the time for insensibility to occur after slaughter in calves, compared with sheep and lambs, is due to a greater contribution of blood to the brain by the vertebral arteries in calves.