Humane-Slaughter-Guidelines

Figure 5—The low atmospheric pressure system is used to stun
poultry via computer-controlled slow decompression. Controlled
and slow precise changes in atmospheric pressure lead to hypoxia
from high altitude simulation and result in a loss of consciousness
and then irreversible stunning of the bird. This system
does not use aversive gas mixtures and eliminates the shackling
of sentient birds since birds remain in their transport containers
during the stunning process.
of EU Council Directive 1099/2009. 48 The method is
currently undergoing commercial testing for broiler
stunning in the United States under a USDA Office of
New Technology Testing Approval. It is not currently
known whether the technology can be adapted for humane
slaughter or depopulation of mammalian species,
such as pigs; however, the insidious effects of altitude
hypoxia on human flight crew performance, including
unconsciousness, are well documented. 49
Low-atmospheric-pressure stunning is not rapid
decompression, as currently deemed unacceptable by
the AVMA Guidelines for the Euthanasia of Animals:
2013 Edition, but rather it is negative atmospheric pressure
applied gradually over time, typically over 1 minute
in broilers, which results in an acute hypoxic state
not unlike being in an unpressurized airplane at higher
altitudes. Maximum observed negative pressure during
commercial broiler LAPS is 23.8 in Hg (604.5 mm Hg a );
this corresponds to an atmospheric pressure of 155.5
mm Hg and an inspired Po 2
of 32.7 mm Hg (assuming
barometric pressure of 760 – 604.5 mm Hg = 155.5 mm
Hg X 0.21 = 32.7 mm Hg oxygen). Thus, LAPS Po 2
at
maximum negative pressure is equivalent to a 4% oxygen
atmosphere at sea level (32.7 mm Hg/760 mm Hg).
For comparison, the atmospheric pressure (P B
) on top
of Mount Everest (elevation, approx 30,000 ft) is 225
mm Hg and the Po 2
is 47.3 mm Hg; at 40,000 ft, P B
is
141 mm Hg and Po 2
is 29.6 mm Hg.
Rapid decompression can cause both pain and distress
through expansion of gases present in enclosed
spaces. 50 In the case of birds, however, gases are unlikely
to be trapped in the lungs or abdomen during
LAPS owing to the unique anatomic structure of the
avian respiratory system and are thus unlikely to become
a source of abdominal distention. Avian lungs
are open at both ends, rigid, and attached to the ribs
and do not change size during ventilation. Attached
to the lungs are nine air sacs that fill all spaces within
the thoracic and abdominal cavities. Because birds lack
a diaphragm, they move air in and out during sternal
movement using the intercostal and abdominal muscles;
air movement is simultaneous and continuous
with no passive or relaxed period. Thus, it is unlikely
significant amounts of gas can be trapped within the
avian lungs or abdomen unless the trachea is blocked
for some reason. 51 In contrast to reports of hemorrhagic
lesions in the lungs, brain, and heart of animals undergoing
rapid decompression, 52 no such lesions were observed
in birds undergoing LAPS. 45 No pathological evidence
of ear damage has been noted in LAPS birds, b and
corticosterone concentrations in LAPS-stunned broilers
were nearly one-half the levels observed in electrically
stunned birds. 45
The LAPS target pressure for broilers is achieved
within 1 minute from the start of the LAPS cycle and
maintained for 4 minutes 40 seconds to assure recovery
does not occur prior to exsanguination. Time to
first coordinated animal movement was 58.7 ± 3.02
seconds, with light-headedness (defined as time from
first head movement to first wing flap) noted within
69.3 ± 6.37 seconds and LOP (an indicator of loss of
consciousness) occurring within 64.9 ± 6.09 seconds.
Neither mandibulation nor deep open-bill breathing
was observed in LAPS birds; bill breathing and mandibulation
are commonly reported during CAS stunning
with various gas mixtures. 13 Wing and leg paddling was
infrequent, lasting 15.1 ±1.12 seconds following LOP. 45
On the basis of EEG studies, increasing slow (delta)
wave activity consistent with a gradual loss of consciousness
occurs within 10 seconds of the start of the
LAPS cycle, peaking between 30 and 40 seconds and
coincident with LOP and first brief movements. 46 The
same research group also determined that heart rate decreases
over time during LAPS, implying minimal additional
sympathetic nervous system stimulation.
A significant advantage of LAPS over electric stunning
and live-dump CAS is elimination of welfare issues
associated with dumping live birds onto the conveyor
line and elimination of manual handling and shackling
of live birds prior to electric stunning. During commercial
operation, birds undergoing LAPS are contained
within palletized shipping cages on transport trucks
in a holding area adjacent to the LAPS cylinders. Pallets
are directly loaded into the LAPS cylinders with a
fork lift. A computer in the control booth controls and
displays the status of the individual LAPS units. Lowatmospheric-pressure
stunning operations are fully automated,
such that once a cycle is initiated, the load
operator cannot override or manually change the LAPS
cycle. Each LAPS cylinder has a video camera mounted
inside that can be viewed in real time on a monitor in
the control booth. Following the LAPS cycle, the palletized
cages containing stunned birds are moved to the
dumping station. After dumping, the birds are moved
by conveyor belt to the shackling area prior to entry to
the processing line. As previously noted, LAPS corticosterone
levels are lower than with electric stunning,
likely owing to elimination of live bird shackling.
T1.2.1 Conclusions
Low-atmospheric-pressure stunning produces a
quiet transition to unconsciousness without escape behaviors
and with minimal physical activity and wing
flapping. Although wing flapping may be observed, it
AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 27