Effective stunning methods are readily available to induce instantaneous insensibility. Good reviews on captive bolt stunning can be found in Leach (1984), Grandin (1994a) and Eikelenboom (1983). Electrical stunning methods used commercially on pigs and sheep are effective and induce instantaneous insensibility. A minimum of 1.25 amps must be passed through a pig's brain to reliably induce insensibility (Hoenderken, 1982). In sheep, 1 amp is required (Gregory and Wotton, 1984).

Unlike pigs and sheep, a single current passed from the neck to the brisket failed to induce epileptiform changes in the electroencephalogram of cattle (Cook et al., 1993). In cattle, a split stun procedure is used. A 2.5 amp current must first be applied to the head before a head-to-body current is applied.(Gregory, 1993). Reviews by Warrington (1974), Leach (1985),Grandin(1985; 1986) and Gregory (1994) provide further information.

• To produce instantaneous, painless unconsciousness, sufficient amperage (current) must pass through the animal's brain to induce an epileptic seizure. Insufficient amperage or a current path that fails to go through the brain will be painful for the animal. It will feel a large electric shock or heart attack symptoms, even though it may be paralyzed and unable to move. When electric stunning is done correctly, the animal will feel nothing.
  

• Simple, easy to build wand for electric stunning of pigs. The front electrode is placed behind the pig's ear. It must not be placed on the neck. The front electrode is curved to fit the shape of the pig and it is 4 inches (10.5 cm) long and 1 inch (2.8 cm) wide.
  

• There are two types of electric stunning, head only and cardiac arrest stunning, which stops the heart. Most large plants use cardiac arrest head to back or head to side of body stunning. It produces a still carcass that is safer and easier to bleed. Cardiac arrest stunning requires the use of a restraining device to prevent the animal from falling away from the stunning wand before it receives the complete stun. Cardiac arrest stunning kills the animal by electrocution. Head only stunning is reversible. Pigs and sheep which are stunned with a head only stunner must be bled within a maximum interval of 30 seconds to prevent them from regaining consciousness. An interval of 10 to 17 seconds is recommended.

• When cardiac arrest stunning is used, one electrode must be placed on either the forehead or in the hollow behind the ears, and the other electrode is placed on either the back or the side of the body. The head electrode should not be allowed to slide back onto the neck. When head only stunning is used, the electrodes may be either placed on the forehead or clamped over around the sides of the head like ear muffs. Pigs should be wetted prior to stunning. The stunning wand must be applied to the animal for two to three seconds to stun properly. Stunners should be equipped with a timer.

• (June 2008 Update): Many very small plants have problems with pigs or sheep returning to sensibility after head only stunning. Their hoist is so slow that bleeding within 10 to 15 seconds is difficult. For plants that use a head only stunner that has two prongs, the following procedure can be used. Apply to the head first to induce insensibility and then apply a second time to the side of the animal right behind the front leg. This is a simple way to convert a head only stunner to a cardiac arrest stunner. To reliably prevent return to insensibility, the heart shock must be applied immediately, within 15 seconds after the head stun. If stunning tongs are used, they can be clamped across the animals' body or applied to the chest. THE HEAD STUN MUST BE DONE BEFORE THE STOPPING THE HEART CURRENT.

• Meat packers should use amperage, voltage and frequency settings which will reliably induce unconsciousness. Both properly and improperly stunned cardiac arrested animals can look similar (Gilbert and Devine, 1991). Current flow through the spine masks the epileptic seizure. If there is any question, electrical parameters should be verified by scientifically valid measurements.

• To prevent bloodspots in the meat and pain to the animal, the wand must be pressed against the animal before the button is pushed. The operator must be careful not to break and make the circuit during the stun. This causes the animal's muscles to tense up more than once and bloodspots may increase. Stunning wands and wiring should be checked often for electrical continuity. A worn switch may break the circuit enough to cause bloodspots. Electrodes must be kept clean to provide a good electrical contact. Operators must never double stun animals or use the stunning wand as a prod.

• Modern stunning circuits use a constant amperage design. The amperage is set and the voltage varies with pig or sheep resistance. Older style circuits are voltage regulated. These circuits are inferior because they allow large amperage surges which can fracture bones and cause bloodsplash. The distance between the head electrode and the back electrode should not exceed 14 inches. Pig stunners should be equipped with blunt electrodes which do not stick into the animal. The most modern sheep stunners from New Zealand utilize water jets to conduct electricity down through the wool.

• Warris et al. (1994) found that pigs were more stressed in abattoirs with single file races compared to plants where pigs were stunned in small groups on the floor. The intensity of squealing was highly correlated with physiological stress measurements and PSE. Electrical stunning of pigs on the floor is most practical for abattoirs that slaughter under 240 pigs per hour. The author has observed that floor stunning often becomes rough and sloppy at higher speeds. In larger plants, a well designed race will produce less stress than a poor one. Weeding et al. (1993) found that both design and staff expertise affected stress levels in pigs.

  

  Pigs move more easily through a ramp where they walk up side by side. The outer sides are solid and the middle partition is "see through" to promote following behaviour.
  

• On the diagram illustrating a well designed pig race, the double chute is recommended. However, if space restriction is an issue, notice the diagram does promote pigs natural following behavior and prevents jamming with an offset step at the entrance of the chute. With the double chute design, the outer walls are solid, with a "see through" middle partition that further promotes following behaviour.

References

Electric Stunning:

Grandin, T. 1985/86 (with 1997 updates)Cardiac arrest stunning of livestock and poultry
Advances in Animal Welfare Science
M.W. Fox and L.D. Mickley (Editors) Martinus Nijhoff Publisher

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