Electroencephalographic studies of stunning and slaughter of sheep and calves: Part 1-The onset of permanent insensibility in sheep during slaughter.

The time of onset of permanent insensibility, subsequent to incision of the major blood vessels of the neck, was studied in sixteen adult sheep and five one-week-old lambs. Insensibility was determined from the study of electroencephalograms (EEG) and interpretation was based on the amplitude and pattern of fast wave signals of a transhemispheric bipolar derivation. In both adult sheep and lambs, conscious at the time of slaughter, insensibility occurred within 2 to 7 s and EEG traces became isoelectric between 10 and 43 s. In sheep which were lightly anaesthetised at the time of slaughter, EEG traces became isoelectric between 18 and 70 s after incision of the major blood vessels of the neck. In one sheep which was slaughtered by severance of the carotid artery and jugular vein on one side of the neck only, the onset of insensibility was delayed for 29 s. In the majority of animals, the electrocardiogram (ECG) continued to show a normal pattern for more than 10 min after slaughter. There was an initial rise in blood pressure in the first 5 to 7 s and it remained elevated for a further 10 to 20 s. The results of this work are discussed with reference to definition of death appropriate for statutory purposes and the implications for the humane slaughter of sheep.