Humane slaughter - Gracey's Meat Hygiene - page 135

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 8 seconds after
the decapitation of a sheep's head, complete pupillary
dilatation does not occur until 87 seconds.
The most reliable objective sign of loss of sensibility is
the absence of respiratory activity . The return of regular
respiratory movements after stunning, but not irregular
respiratory gasps, should always be a cause of concern.
'Gagging' respiratory movements, agonal breathing, are
generally a sign of imminent brain death. In general,
vocalisation in animals during the induction of uncon-
sciousness with any stunning method is indicative of
pain or suffering. Absence of vocalisation does not how-
ever guarantee absence of pain or suffering.

12-30 seconds (average 18 seconds) and cattle in 20-102
seconds (average 55 seconds). The species differences are
due to differences in the arteries which supply the blood to
the brain via the Circle of Willis. In all cases, in the interests
of the animal, it should be assumed that the upper limit
applies.
Electroencephalograms (EEGs) and electrocortico-
grams (EcoGs) are widely used to record brain electrical
activity in order to determine the state of consciousness.
Efficient stunning methods disrupt the neurons or neu-
rotransmitter regulatory mechanisms in the brain. EEG
brain wave patterns show changes from the normal which
are incompatible with consciousness, such as grand mal
epilepsy or prolonged periods of quiescence. In addition,
external stimuli fail to evoke electrical activity in the
brain (somatosensory evoked potentials) indicating the
brain's incapacity to receive and process external stimuli.
Within the abattoir however, observation of clinical
signs is the only method available to assess an effective
stun. The typical signs of effective stunning by electricity
are immediate collapse of the animal with flexion, fol-
lowed by rigid extension of the limbs, opisthotonus
(extreme arching back of the neck and spine), downward
rolling of the eyeballs with tonic (continuous) muscular
spasm changing into clonic (repeated) violent spasms
and eventual muscle flaccidity. The term electroplectic fit
has been used to describe these signs of an effective stun .
The tonic spasms last for some 10-25 seconds, and the
clonic phase 15-45 seconds, in both pigs and sheep.
The typical signs of an effective stun using concussive
methods in cattle are immediate collapse of the animal fol-
lowed by tonic spasm lasting about 10-15 seconds, then
slow clonic movements of the hind legs and eventually
vigorous hind leg movements. In pigs, the tonic phase lasts
3-5 seconds, followed immediately by violent, clonic mus-
cle spasms which make bleeding the animal difficult and
often dangerous. In an effective stun, normal rhythmic
breathing must cease immediately, and the eyeball should
face outwards with a fixed gaze and not be rotated inwards.
In carbon dioxide anaesthesia in pigs , the effects are
those of a chemical anaesthetic, with the eventual onset
of insensibility. A period of increased respiratory rate is
followed by slow respiratory movements and final dysp-
noea (difficult breathing). Corneal and palpebral reflexes
are absent, and extreme muscle flaccidity supervenes.
The limbs and jaw are consequently relaxed.
The use of palpebral, corneal or pupillary reflexes to
ascertain the effectiveness of stunning is inappropriate
for most methods of stunning. Palpebral and corneal
reflexes are not under cortical control and may therefore
be present in an animal or bird which has been rendered
insensible. Conversely, the palpebral reflex may be absent
in an animal which has been ineffectively electrically
stunned. Although complete pupillary dilatation is a

Methods of stunning
The choice of a particular method of stunning depends
on many different factors - species, breed and age of ani-
mal, intended line speed, humane aspects, capital and
maintenance costs, efficiency of equipment, ease of
operation, safety of personnel and effects on carcase and
brain, along with religious and legal requirements.
The number of variable factors involved in modern
stunning systems, especially electrical and gaseous meth-
ods, makes a system of approval prior to operation desir-
able. The parameters under which a particular system
operates should be recorded; for example, the required
line speed, class of animal, current as measured in average
amps, waveform and frequency. Methods by which the
system's operation is measured, calibration of the moni-
toring equipment, records to be completed and audited
should also be agreed with the competent authority.

Percussive stunning
Many different types of percussive stunning pistol are in
use throughout the world, having been introduced at the
end of the nineteenth century. They are generally oper-
ated by means of a blank cartridge, although some are
pneumatic in design. With the most common type, the
captive bolt pistol , a bolt is propelled forward on discharge
of the blank cartridge and automatically recoils into the
barrel. The tip of the bolt is concave and has a relatively
sharp rim. Ideally, the bolt, which varies in length from
70 to 121 mm and in diameter from 12 to 14 mm, should
be recessed into the body of the pistol so that when the
muzzle is held firmly against the animal's head, the bolt
can gain velocity before penetration of the skull occurs.
It is important when using captive bolt pistol to ensure
that the correct strength of cartridge is used for the dif-
ferent species. With Cash instruments, these range in
strength from 1 grain for small animals such as milk