43
adult cattle in a turning pen, revealed that effective stunning and permanent insensibility can be achieved with precise electrode placement plus a skilled cut performed within 5 to 8 seconds after the end of a 4 seconds current flow. During the cut the animals were still well restrained in the rotary pen. Thus the second problem mentioned above – the clonic convulsions – can be managed by means of restraint and immediate cutting, or by electroimmobilisation with low voltage spinal discharge (Wotton et al., 2000; Devine et al., 1987; Devine et al., 1986b). However this may mask potential signs of returning consciousness. The recommended minimum amperage is 1.5 amperes for adult cattle and 1.3 amperes for calves up to 6 month of age. In practice depending on the construction and placement of electrodes often 2 to 3 ampere are applied in cattle. Voltages used are 350 to 400 Volts. Electrode position for handheld tongs is preferably temporal between the eye and the ear. With automatic current application the current flows through the brain between neck electrodes and a nose plate. Current should be applied for at least 4 seconds to the head (EFSA, 2004, page 70). If ventricular fibrillation is to be induced at least 1.5 amperes are recommended for cattle and about 1.0 ampere for calves, applied for minimum 5 seconds, but in practice again often higher currents and longer application times are used (EFSA, 2004, page 70). Under routine conditions effectiveness of electrical stunning however may be low, due to technical shortcomings. Aichinger (2003) reported that 10 percent of 619 cattle stunned by a Jarvis beef stunning device with automatic application of a 4 second head current and subsequent induction of ventricular fibrillation were re-stunned by captive bolt. Although the staff tended to re-stun cattle which could be considered unconscious the percentage of cattle showing focused eyeball movements and regular breathing was due to very late sticking after shackling. In another investigation of head only electrical stunning 9 of 23 cattle were considered insufficiently stunned by showing eye tracking of stimuli and coordinated leg movements. In this case the cause was presumably a low voltage of only 250 Volts and bad sticking quality was presumably the reason (Stueber, 2000). In sheep and goats the main principles apply as for cattle, as described by EFSA (2004, page 77 ff.) and Blackmore and Delany (1988). The tongs should be positioned between the eyes and the base of the ears on both sides of the head preferably on local wet skin. Wool, dry skin and placement of the tongs in a caudal position behind the ears, lowers stunning effectiveness (Velarde et al., 2000). Pointed electrodes (electrodes with pins) give good grip and electrical contact, because they penetrate the wool. Electrodes with serrated edges may work in shorn sheep and if the area of application is moistened. With small areas of contact between the sheep’s head and the electrodes, wool-burning and marked carbonising of the electrodes can occur. This, in turn, leads to a poor electrical contact due to an increased electrical resistance in the pathway and special care is necessary to keep the electrodes clean. Effective head-only stunning in sheep should be induced using minimum currents of 1.0 Ampere. A minimum of 250 Volts should be used to deliver the current. Duration of current flow should be a minimum of 2 seconds. The maximum stun-to-stick interval is 8 seconds (EFSA, 2004, page 78). Following anecdotal reports for mature sheep even higher intensities of current about 1.3 to 1.5 Amperes may be necessary to achieve sufficient stunning effectiveness. Currents used in sheep in practice often have a higher frequency than 50 Hertz, e.g. 100 or 400 Hertz and also current patterns are used where the frequency decreases during current application from 500 Hertz to 100 Hertz. In order to check for clinical signs of correct stunning and recovery in sheep, the safest indicators are the typical pattern of seizures and return of normal rhythmic breathing. Resumption of rhythmic breathing can occur during the second clonic phase, as in lambs the