Effective Stunning

An effective stun is dependant, amongst other things, on the blow being administered to the correct part of the skull. In order to ensure maximum impact on the brain, the best position is where the brain is closest to the surface of the head and where the skull is at its thinnest. In most animals this is the frontal region of the head. The ideal position and direction of impact varies between species, within species, and according to whether the equipment is penetrative or non-penetrative. To obtain maximum effect, the muzzle of the captive-bolt stunner must always be held firmly against the head.

Figure 5: Lateral view of a mammalian brainKey: Upper brain/cerebral cortex (1), Mid-brain/cerebrum (2), Brainstem/medulla oblongata (3), Spinal cord (4)

Failure to stun

If an animal is not properly stunned it must be re-stunned immediately. When a captive-bolt enters the skull it causes massive damage and swelling around the wound; the swelling will absorb much of the impact of the second shot and this will mean the shock wave is not as effectively transmitted to the brain. A repeat shot must always be placed so as to avoid the immediate area of the first shot. If the first shot is off target, the second should be placed as close to the correct stunning position as possible. If the first shot is on target but fails to produce an effective stun, the second shot should be above and to one side. If a third shot is required, this should be above and to the other side of the first shot. Once stunned, the animal should be bled or pithed without delay.

Operator considerations

Experienced slaughtermen will have their own preferences for the way in which animals are presented for stunning. The operator should not have to concentrate on keeping his balance, or have to bend excessively each time he stuns an animal, as this becomes tiring and can lead to inaccurate stunning. Stunning pen and conveyor design is therefore of utmost importance for both animal welfare and the operator’s health and safety.

In general, it is easier if the stunning box or restrainer-conveyor presents the animal to the slaughterman’s favoured side, i.e. right-handed or left-handed. The system should also be designed so that the slaughterman does not have to bend right over to carry out the stunning operation. However, the sides of a stunning box must be high enough to prevent large cattle jumping out before they are stunned. Alternatively, overhead restraint bars must be fitted.

Where an air-powered captive-bolt stunner is used with a restrainer-conveyor, it should be properly counterbalanced above the stunning point so that it returns to the ‘resting’ position without the slaughterman having to lift it.