Electroencephalographic studies of calves associated with electrical stunning, throat cutting and carcass electro-immobilisation

Abstract

Electroencephalographic (EEG) recordings were made on 34 calves (two days to six weeks old, 30–50kg) during the slaughter process. The calves, supported in a V-shaped box or polypropylene net, were either head-only electrically stunned (50 Hz, 1.0A) across the head and allowed to recover, head-only stunned followed by throat cutting or head-only stunned followed by throat cutting and electro-immobilisation. All time intervals were measured from the commencement of the stun. The electro-immobilisation (80 V peak, 14.3 Hz, 5ms square wave) at 15–26 seconds post-stun was applied through electrodes attached to nose and anus, for periods ranging from 5–60 seconds.

The head only stun produced an elevated EEG amplitude of the electroplectic fit which lasted approximately 34 seconds followed by a quiescent period before the EEG amplitude again became elevated above normal. A normal pre-stun pattern was not reached until many minutes had elapsed. Following the stun, the forelegs were usually flexed and then extended, gradually becoming part of the paddling movements commencing as early as eight seconds post-stun. Such movements were taking place while the animal was still stunned. With a head-only stun followed by throat cutting, the electroplectic fit was reduced to about 23 seconds and the amplitude of the EEG fell to about 10μV after 50–73 seconds and breathing was inhibited for at least 20 seconds after stun commencement. If inadvertently only one carotid was severed, the EEG did not fall as rapidly as when both carotids were cut.

The increase in amplitude of the EEG tracings was caused by stunning but the reduced duration of this increase in calves in which the throat was cut, suggests that there is an impairment of recovery of brain function from the moment of cutting and recovery of sensibility is unlikely.

In reviewing the criteria of sensibility, we believe that insensibility can be presumed to continue from stun initiation, through the throat cut until the EEG falls below 10 μV provided that there is no resurgence of activity and the EEG amplitude continually falls rapidly enough. By this criteria, calves which are electrically stunned and rapidly exsanguinated remain permanently and irreversibly insensible. The addition of at least 15 seconds electro-immobilisation causes an even more rapid fall in the amplitude of the EEG (<10 μV at 50 seconds) making insensibility more certain as well as abolishing animal movement.