Humane-Slaughter-Guidelines

Figure 4—Animals are moved on continuous conveyors through
a tunnel (as shown) or into a pit containing a heavier-than-air gas
in open CAS systems.
than air and, therefore, difficult to contain. Also, closed
CAS systems use a greater volume of stunning gas than
open systems because the stunning area must be evacuated
prior to loading the next group of animals.
Detection of problems
Some of the most common problems are CO 2
concentration
that is too low or insufficient dwell time in
the chamber. These problems can result in either return
to sensibility on the slaughter line or stressful anesthetic
induction. Insufficient dwell time is most likely to occur
in plants that have undersized equipment. Many CO 2
systems have automated powered gates to move animals
into the chamber. There is a serious problem if the automated
gates either knock animals over or drag them
along the floor. If these gates cause more than 1% of the
pigs to fall, that exceeds the industry voluntary guideline.
34 If powered gates drag animals, that is a violation
of the HMSA. Another problem is overloaded gondolas
where animals do not have room to stand without being
on top of other animals. This is most likely to occur in
equipment that does not have sufficient capacity.
Corrective action for problems
1. Maintain a CO 2
concentration of over 80%. A 90%
concentration at either the bottom of the pit or at
the final stage of the process is strongly recommended.
2. Increase dwell time if there are problems with return
to sensibility.
3. Undersized equipment that has insufficient capacity
is often the cause of insufficient dwell time or
handlers overloading the gondolas with animals.
Either a larger piece of equipment or an additional
unit will be required to increase system capacity.
4. The pigs or poultry must have sufficient room in
the gondolas or container to stand or lie down
without being on top of each other.
5. When automated gates are used to move pigs up
to and into the chamber, they must be equipped
with pressure-limiting devices. This prevents the
gates from knocking animals over or dragging
them along the floor. Often, powered gates work
best when they are equipped with a push button
or other control that allows the handlers to control
forward movement of the gate. When the handler
lets go of the control, the gate stops. An automated
control works well to return the gate to its start
position after it has moved the animals.
6. Ventilation problems in the plant building can
sometimes cause CO 2
to be sucked out of the
chamber. Some commercial CO 2
equipment holds
CO 2
in a pit that is not sealed, and sometimes, air
pressure changes in the plant building can cause
sensible pigs or birds to emerge from the chamber.
Some of the factors that can suddenly lower CO 2
concentration are either turning off or turning on
large ventilation fans in the plant building, wind
blowing around the plant building, or leaving certain
plant doors open. Careful observation will be
required to correct this problem. It is often correctible
and no equipment purchases are required.
T1.1.2 Conclusions
For humane slaughter of poultry, initial exposure
to lower CO 2
concentrations and a gradual increase of
CO 2
concentrations produce a smoother induction of
unconsciousness and reduce convulsions, compared
with anoxia with N 2
and Ar. Carbon dioxide may invoke
involuntary (unconscious) motor activity in birds,
such as flapping of the wings or other terminal movements,
which can damage tissues and be disconcerting
for observers; however, wing flapping is less with CO 2
gas mixtures than with N 2
or Ar. For humane slaughter
of pigs, exposure to > 80% CO 2
is recommended.
Compared with electric stunning methods, CAS for
poultry presents some animal welfare advantages because
manual handling and shackling of live birds are
eliminated. Some gas mixtures may cause unacceptable
escape behaviors, such as attempting to climb up the
sides of the container or vigorous flapping in chickens
before LOP. In addition, CAS can also eliminate welfare
issues associated with dumping live birds from
their transport cages prior to stunning; however, this
depends on the design and implementation of CAS at
the processing plant. Controlled atmosphere stunning
for pigs and lambs may also improve animal welfare by
reducing animal handling.
T1.2 Low Atmospheric Pressure
Low-atmospheric-pressure stunning (Figure 5) is
a recently described method for stunning birds prior
to humane slaughter. Unconsciousness due to hypoxia
occurs following a controlled and gradual reduction
of barometric pressure. 44–46 At one time the European
Union allowed the use of a vacuum chamber for
slaughter of farmed quail, partridge, and pheasant, 47
however this approval was revoked with the adoption
26 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition