1. The stunner operator's station must be kept dry.

2. Stunning wands should be designed so that they can be operated by one hand. Avoid designs where the two electrodes are held separately in each hand. These increase a shock across the chest electrocution hazard.

3. The operator should wear rubber boots and stand on non-conductive plastic grating.

4. The restrainer frame and worker walkway structure should be grounded to a perfect ground. However, the side of the restrainer that the stunner operator can touch should be covered with heavy insulating materials such as a plastic meat cutting board.

Electrical stunning methods used commercially on pigs 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).

• 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.
  

• 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 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.

• 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 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.
  Good example layout for pigs

• 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.

Grandin, T. 1985/1986 Cardiac Arrest Stunning of Livestock and Poultry
in:M.W.Fox and L.D.Mickley (Editors)
Advances In Animal Welfare Science
Martinus Nijhoff, The Hague, The Netherlands

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