Humane-Slaughter-Guidelines

eturning to consciousness after head-only stunning
because of slow hoisting procedures. To prevent return
to consciousness, a second current should be applied
to the body immediately after initial head stunning to
stop the heart. 120 Proper restraint is critical to allow the
correct placement of the electrodes. Electrodes should
be cleaned daily and properly maintained.
Improper electric stunning of sheep and pigs
can cause blood splash, pale muscle color, or broken
bones. These problems are a meat-quality issue and
not an animal welfare concern because passage of the
current through the brain has already induced unconsciousness.
The tongs or wand should be pressed firmly
against the animal before the current is turned on. If the
wand is energized before it is firmly applied, pigs will
produce a short squeal but sheep will remain silent. 34
This is a welfare concern because the animal would feel
the shock. When the wand or tong is only partially applied,
the animal does not receive the full amount of
current. 130 Electric stunners work best when they are
equipped with an automatic timer.
Poultry
Electric stunning is the most universally accepted
and used method for stunning prior to slaughter for
poultry. 103 The most widely used method for electrostunning
poultry is the electric water-bath stunning
method (Figure 14), which involves the direct contact
of the bird’s head in an electrified water bath. Birds
are shackled and, while suspended upside down, pass
through a water bath. Each bird is immediately stunned
for a period that lasts between 30 and 60 seconds. 131
Efficacy of the water-bath system is influenced
by the species, number, and size of the birds passing
through the water bath because with increasing size
and number of birds in the bath at one time the resistance
increases and because parallel paths of current
arise with increasing numbers of birds. Variable resistance
can result in insufficient current to produce immediate
unconsciousness. Constant-current stunners
may alleviate this problem. 132
Smaller commercial facilities may use a handheld
stunner for electrically stunning birds. When this
method is used, birds must be properly restrained and
held. Electrodes must be properly constructed to ensure
contact with skin through the bird’s feathering.
Placing water on the head of the bird reduces resistance
and enhances the stunning process.
Welfare issues for electric stunning of poultry exist.
Birds must be handled carefully, as the shackling
procedure may be distressful and painful. 133 If wing
flapping occurs immediately prior to the entrance of
the water-bath stunner, preshocks from the stunner
can occur. 134 Breast rubs, low lighting, and a smooth
transition into the stunner can reduce the frequency
of wing flapping. Proper stunner design, including a
nonconductive entrance, will also help eliminate prestun
shocks. Shackles must be of the appropriate size
for the species and specific birds. If handheld stunners
are used, then appropriate placement of the electrodes
between the ears and eyes is essential. Because of the
variable resistance between species, flocks, and even
individual birds, recommendations for optimal electric
Figure 14—In electrical water-bath stunning, birds are shackled,
and while suspended upside down, the bird’s head comes into
direct contact with an electrified water bath.
parameters for effective stunning in poultry are difficult
to make 135 :
United States model—Contrary to the European
model, electrical stunning in the United States involves
pulsed direct current with low current (25 to 45 mA/
bird), 103 low voltage (10 to 25 V), 103,136,137 and high frequency
(approx 500 Hz). 103,136,137 This type of system
became possible with advances in electrical circuitry
and changes to the length of the water bath cabinet that
increase dwell time of the birds and decrease the total
resistance in the water bath. 103 In a survey of 329 US
poultry plants, 92.1% reported using electrical stunning
and 77.4% of those plants used low-voltage (10 to
25 V), high-frequency (500 Hz) systems. 121
Behavioral reactions
Efficacy of the stunning in US slaughter plants has been
determined by assessing corneal and comb reflexes. 121
Typically, a bird is considered stunned by plant personnel
when it becomes unresponsive to stimulation of
the cornea or comb with its eyes wide open, an arched
neck, and tucked wings. 121 One study 138 evaluated a
2-phase step-up stunner, with a first phase consisting
of low-voltage (12 and 15 V), high-frequency (550
Hz) pulsed direct current for 10 seconds and a second
phase consisting of sinusoidal wave alternating current
(50 Hz at 40, 50, and 60 V for 5 seconds). 138 The best
results for this combination occurred in male birds at
the highest voltage settings (phase one, 15 V; phase
two, 60 V). 137 Under these conditions, only 22% of the
birds had corneal reflexes, 18% had spontaneous blinking,
and < 10% had wing flapping. 138
Physiologic reactions
One study 138 that evaluated a 2-phase step-up stunner,
with a first phase consisting of low-voltage (12 and 15
V), high-frequency (550 Hz) pulsed direct current for
10 seconds and a second phase consisting of sinusoidal
wave alternating current (50 Hz at 40, 50, and 60
V for 5 seconds), found that 45% of the birds did not
achieve an isoelectric EEG. Contradicting this, another
research group evaluating a similar 2-phase step-up
stunner (phase one, 23 V [550 Hz direct current for 10
seconds]; phase two, 15 V [60 Hz alternating current
for 5 seconds]) found that the poststunning EEG had
a brief period of high-amplitude spikes that progressively
decreased in amplitude over time. h These investigators
found the EEG recording of the brain activity
to be very similar to that seen with the European model
of electrical stunning. h Summary
Results of studies of birds stunned with the low-voltage
US model indicate that the birds are unresponsive to
AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 37