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Abstract
The effects of various aspects of electrical stunning and slaughter were studied in more than 4,000 sheep and calves, the majority of which were being processed in different New Zealand meat export works.
Electrical stunning must induce cardiac dysfunction to ensure that sheep and lambs do not regain sensibility during currently employed slaughter processes. Electrical stunning by both “head-to-back” and “head-to-leg” methods produces cardiac inhibition provided that electrodes are properly positioned and sufficient electrical current is applied. Electrocardiograms (ECG) of electrically stunned animals demonstrated that cardiac dysfunction can be readily detected by the use of stethoscope. The reactions of stunned and slaughtered animals to various nervous stimuli are unreliable determinants of insensibility. Slaughter of sheep, stunned by a “head only” method, by a lateral stab incision of the neck is unsatisfactory. In more than 14% of the animals the blood vessels were incised only on one side of the neck and in more than 30% the oesophagus was incised. The rate of bleeding was reduced in those animals stunned by a method which caused cardiac dysfunction but there was little effect on the total amount of blood lost from the carcase.
The prevalence of petechial haemorrhages in the fat (“speckling”) of lamb carcases was significantly increased in lambs stunned by a “head-to-leg” method when the forelegs were not in contact with the leg electrode.
The significance of these findings is discussed in relation to humane and economic considerations.