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TYPICAL SIGNS OF UNCONCONSCIOUSNESS DUE TO STUNNING
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In the act of slaughter it is essential that a state of unconsciousness or insensibility be instantaneously produced to ensure total freedom from suffering, this being further ensured by immediate exsanguination.
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Where cardiac arrest has been created there is an almost immediate insensibility, which is permanent.
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The discovery that adequate bleeding ensues despite cardiac dysfunction in this method makes this a most important development in the slaughter of animals.
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It has been always thought that a beating heart was necessary for proper bleeding, but this has been discounted provided sticking is performed soon afterwards.
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The time taken to reach insensibility due to exsanguination depends upon the technique utilised in sticking, the species, the age of the animal, whether the carcass is suspended or method of pre-stunning used.
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Based on electroencephalographic data, sheep have been shown to become insensible in 2-7 seconds, pig in 12-30s (average 18s) and cattle in 20-120s (average 55 s).
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The species differences are due to differences in the arteries, which supply the blood to the brain via the Circle of Willis.
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In all cases, in the interests of the animal, it should be assumed that the upper limit applies.
The typical signs of effective stunning by electricity
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The immediate collapse of the animal with flexion, followed by rigid extension of the limbs, ophisthotonus (extreme arching back of the neck and spine), down ward rolling of the eyeballs with tonic (continuous) muscular spasm changing into clonic (repeated violent) spasms and eventual muscle flaccidity.
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The term electroplectic fit has been used to describe these signs of an effective stun.
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The tonic spasms last for some 10-25s, and the clonic phase 15-45s, in both pigs and sheep.
The typical signs of an effective stun using percussive methods
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Cattle are immediately collapsed followed by tonic spasm lasting about 10-15s, and then slow clonic movements of the hindlegs and eventually vigorous hindleg movements.
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In pigs the tonic phase lasts 3-5 s.
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Normal rhythmic breathing must cease, and the eyeball should face outwards with a fixed gaze and not be rotated inwards.
The typical signs of effective stunning by carbon dioxide
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In pigs the effects are those of a chemical anaesthetic, with the eventual onset of insensibility.
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A period of increased respiratory rate follows slow respiratory movements and final dyspnoea (difficult breathing).
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Corneal and palpebral reflexes are absent and extreme muscle flaccidity supervenes.
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The limbs and jaw are consequently relaxed.
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The use of palpebral, corneal or papillary reflexes to ascertain the effectiveness of stunning is inappropriate for most methods of stunning.
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Palpebral and corneal reflexes are not under cortical control and may therefore be present in an animal or bird, which has been rendered insensible.
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Conversely, the palpebral reflex may be absent in an animal, which has been ineffectively electrically stunned.
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Although complete papillary dilatation a reliable sign of total insensibility of an animal nearing the point of death, it is of little practical use since, for example, it has been demonstrated that while sensibility as measured by electrical activity occurs 8s after the decapitation of a sheep’s head, complete papillary dilatation does not occur until 87s.
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The most reliable objective sign of loss of sensibility is the absence of respiratory activity.
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The return of regular respiratory movement after stunning, but not irregular respiratory gasps, should always be a cause of concern.
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‘Gagging’ - respiratory movements are generally signs of imminent brain death.
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