Assessment of Return to Consciousness After Electrical Stunning in Lambs

The return to consciousness of 24 electrically stunned lambs was assessed by measurement of physiological reflexes and electroencephalography (EEG) recordings. The physical activity of the lambs after head-only electrical stunning included one tonic phase and two clonic phases. The tonic phase began immediately after the stun and ended 10 s after the stun; the first clonic phase started immediately after the tonic phase and ended 36 s after the stun, and the second clonic phase started immediately after the first clonic phase and ended 70 s after the stun. During the tonic phase and the first clonic phase, electrical activity recordings of the brain showed a dramatic increase in the relative power spectra of alpha and beta frequencies. Both frequencies returned to pre-stun levels with the end of the first clonic phase. During the second clonic phase, the relative power spectrum of theta frequency was higher than that before stunning. These results suggest that during the tonic phase and the first clonic phase, the animal was unconscious, whereas during the second clonic phase the return of some conscious function began. Spontaneous breathing returned at about 29 s post-stun, whereas the corneal reflex returned at about 38 s. It is therefore suggested that the return of spontaneous breathing is the safest indicator that the animal is close to recovering consciousness.