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achieved by blood loss following slaughter and not by the stunning method itself, because blood loss from sticking has a more immediate effect on the brain. In the following subsections the focus is on stunning methods which are applied during religious slaughter. Table 6: Stunning methods used in the context of religious slaughter Species Stunning method Electrical head only stunning Penetrating captive bolt stunning Non-penetrative captive bolt stunning Gas stunning 1 2
Cattle X X X
Sheep and goats X X X2
Poultry (chicken and turkey) X1 X2 X X
Current also applied through the whole body but without induction of ventricular fibrillation Not in general use
4.2.1
Electrical stunning
Electrical stunning causes unconsciousness and insensibility by producing a depolarisation shift in nerve cells followed by hyperpolarisation of action potentials which leads to epileptiform discharges (Gregory, 1987b). If an electric current is applied to the head, and sufficient current flows through the brain, unconsciousness occurs in a similar manner to that produced in grand mal epileptic seizure. There is disordered metabolism and electrical activity, which cannot support conscious activity (Gregory, 1998a). Grand mal epilepsy is a pathological extreme of neuronal synchrony and is considered to be incompatible with normal neuronal function and, hence, persistence of consciousness (Cook et al., 1995; Cook et al., 1992; Hoenderken, 1978). The electrical current flow through the head has been considered painful (Rosen, 2004), though Levinger (1976) admits that in most cases where electric shock therapy is used in humans the patient loses consciousness before he feels pain. It is true that a poor initial contact, a slow rise in current levels or insufficient peak current levels, may not stun the animal immediately and it could be experienced as a painful electric shock. However it is known, that when electrodes are properly placed with the necessary minimum current that within far less than one second synchronization of electric potentials in the brain is achieved. This disrupts all coherent processing of information by the brain before electric shocks can be sensed as painful. After the current has been maintained for a given time the nerve cells are unable to react to further stimulation in a way that can be associated with consciousness (Gregory, 1987b; Hoenderken, 1978; Warrington, 1974). The effects of the current flow at the neuro-chemical cellular level are now well understood. Neurotransmitters enable the communication between neurons in the brain. Excitatory (Glutamate/Aspartate) and inhibitory (GABA) neurotransmitters interact to form a physiological equilibrium. After the electrical current flows through the brain there is a dramatic rise in the extracellular concentrations of Glutamate and Aspartate. The cell structures are in a state of heightened excitation and uncoordinated activity. The interruption in the processing of signals leads to an immediate loss of consciousness (within 200 ms (Cook et al., 1995)). The slower release of GABA during the course of the epileptiform fit brings the fit to an end. Because elevated concentrations of GABA can also be due to stress and elevated GABA levels can inhibit the effects of Glutamate/Aspartate, stress can negatively influence the ability to produce epilepsy. This illustrates the importance of careful handling of animals prior to stunning. The elevation of the extracellular concentration of GABA lasts significantly longer than that of Glutamate/Aspartate and contributes to a long lasting analgesia after the electrical stun (5-15 min). The role of the neurotransmitters in electrical stunning was clarified in earlier experiments with pharmacological agonists and antagonists. These findings