Humane-Slaughter-Guidelines

time to unconsciousness. Animals stunned using higher
frequencies will regain sensibility more quickly. 110 In
other studies, 98,107,111 frequencies of 2,000 to 3,000 Hz
failed to induce unconsciousness. Grandin 107 recommends
that higher frequencies only be used when they
are passed through at least two electrodes to the head.
Frequenices of sine waves at 1,592 Hz or square waves
at 1,642 Hz are effective in pigs, but the period of unconsciousness
will be shorter. 110 Eight hundred hertz
applied to the head with 50 Hz applied to the body is
also acceptable. 112
Proper electric stunning must not be confused with
electric immobilization that paralyzes an animal without
inducing unconsciousness. 113 Immobilization without
unconsciousness is highly aversive and must not be
used. 114,115 Electrocution induces death by cardiac fibrillation,
which causes cerebral hypoxia. 99–101 However, animals
do not lose consciousness for 10 to 30 seconds or
more after onset of cardiac fibrillation. It is imperative
that animals be unconscious before being electrocuted.
T2.2.2 Methods
Three methods are used to perform electric stunning:
the head-only reversible method; the one-step
head-to-body cardiac arrest method; and the two-step
method consisting of a current applied only to the head,
followed by a current applied to the body, which stops
the heart. 116 The head-only method does not cause cardiac
arrest and will result in a return to consciousness
in 15 to 30 seconds. 59,117 In the head-only method, animals
should be bled within 15 seconds. 117 Tongs must
be placed so that the current goes only through the
head, which can be accomplished by placing tongs either
on both sides of the head or on the top and bottom
of the head (Figure 11).
The one-step method uses current applied through
the head to the body to induce cardiac arrest. Current is
simultaneously passed through both the brain and the
heart, which induces cardiac fibrillation and immediate
loss of consciousness (Figure 12). 59,116 Wotton and
Gregory 118 suggest that the induction of cardiac arrest
provides a major animal welfare advantage because it
promotes the start of death. Use of the head-to-body (or
–chest, -back) method has been shown to be highly effective
in inducing irreversible unconsciousness in over
98% of pigs evaluated. g Pork plants using V-shaped conveyor
restrainers have achieved > 99% correct electrode
placement when the one-step head-to-body cardiac arrest
method is used. 119 Grandin 108 recommends when
the one-step method is used that the first 1-second
treatment should be at least 1.25 A at 50 to 60 Hz. One
electrode must be placed on the head, and the other
electrode can be placed on any part of the body (except
for sensitive areas such as the eye, ear, or rectum). The
first electrode must not be placed on the neck or the
back of the neck because the current will bypass the
brain and cause instant pain.
The two-step method (Figure 13) uses the headonly
method followed by a second application of the
tongs to the chest. This method causes unconsciousness
first and then death by cardiac arrest. Applying the
second current by placing the electrode on the chest
behind the foreleg has been reported to be effective. 120
Figure 11—Proper electrode placement for the head-only electric
stun method.
Figure 12—Proper electrode placement for the one-step (headto-body)
electric stun method, where the current is passed simultaneously
through both the brain and the heart. The head
electrode may be placed on the forehead or immediately behind
the ear (as shown).
T2.2.3 Signs of effective stunning
Unconsciousness occurs when electricity inhibits
impulses from both the reticular activating and the somatosensory
systems of the brain. 121 Signs of effective
seizure induction include extension of the legs, opisthotonus,
and downward rotation of the eyeballs as
AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 35