Humane slaughter - Gracey's Meat Hygiene - page 147

Electrocorticogram (EcoG) is elicited within a few sec-
onds, corneal reflexes remain in completely isolated
heads for periods up to 30 seconds. In his commentary
article, Bates (2010) concluded that

but the birds show none of the behavioural signs, such
as gasping and head shaking, associated with the irri-
tant properties of CO 2 (Raj and Gregory, 1993, 1994). It
is recommended that birds should be exposed to the
gaseous environment for a minimum of 2 minutes and
that hanging and neck cutting in broilers should be car-
ried out within 3 minutes of gas stunning if carcase
defects such as red wing tips, wing vein engorgement/
haemorrhage, shoulder haemorrhage and red feather
tracts are to be minimised. However, gas stunning does
result in fewer broken bones than electrical stunning,
especially the broken wing bones which can enter the
breast muscle, the so-called chokers; and breast muscle
haemorrhages are eliminated.
It has been discovered that stunning with argon-
induced anoxia accelerates the fall in muscle pH during
the early post-mortem stage without inducing a PSE-like
condition. Used in conjunction with air chilling at 1°C,
filleting can be performed at 2 hours post-mortem. The
eating quality of this meat was rated in tests as superior
to that of control fillets.

1 Severing the spinal cord and the tissues immediately
surrounding is likely to be painful.
2 Decapitation is a painful procedure and that conscious
awareness may persist for up to 29 seconds in the dis-
embodied heads.

Effects of stunning on poultry meat quality
As with the larger farm animals, deleterious changes
sometimes occur in poultry carcases after slaughter
which are attributed to defects in the slaughter methods.
These frequently result in downgrading and even con-
demnation. However, conclusions about the effects of
stunning are often contradictory and at least some of the
changes encountered may be occasioned by the stress of
handling and transport in part, if not in whole.
A disadvantage of using 50Hz AC water bath stunners
is that, at current levels greater than 105 mA per chicken
and 150 mA per turkey, there are significant increases in
the incidence of haemorrhaging in the breast and leg
muscles, broken bones in the carcase and the appearance
of other conditions which result in carcase downgrading
(Gregory and Wilkins, 1989a, 1989b).

Percussive stunning of poultry
Percussion stunning using both penetrative and non-
penetrative captive bolt results in severe skull fractures
and structural damage to the brain of poultry. A com-
mercially available captive bolt device fitted with a non-
penetrating percussive head is used to kill poultry on
farm and as a backup method in commercial poultry
slaughter establishments. When penetrative captive bolts
are used, the bolt diameter, velocity and penetration
depth are critical to achieving a humane stun/kill. The
captive bolt should be fired perpendicular to the frontal
bone surface with the bird restrained, usually in a cone,
and the head supported by the operative's hand. The bolt
diameter should be a minimum of 6 mm. Signs of an
effective stun include uncontrolled and severe wing flap-
ping, immediate loss of breathing, loss of neck tension,
leg flexion and extension.

Pithing
After cattle are stunned, they were sometimes pithed
before bleeding by the insertion of a long thin rod or
closely coiled wire into the hole made by the penetrating
bolt of the pistol. The insertion of this rod destroys the
motor centres of the brain so that reflex muscular action
does not occur at sticking, thus avoiding injury to opera-
tives and speeding carcase dressing. There is little evi-
dence that this operation interferes with the bleeding of
the carcase to any appreciable degree, but the pithing rod
or cane should not be any longer than 0.6 m; if it is too
long, the spinal cord roots of the greater splanchnic nerve,
which is the main vasoconstrictor of the abdominal cav-
ity, are destroyed. The resultant dilatation of the splanch-
nic blood vessels causes congestion of the liver, kidneys
and intestines and, in addition, congestion and enlarge-
ment of the spleen, producing the ' slaughter spleen '.
Pithing was used with the bed system of carcase dress-
ing. Under modern conditions, where cattle carcases are
suspended for dressing, it is completely unnecessary pro-
vided efficient stunning and shackling are carried out,
besides being very unhygienic and time-consuming .
Pithing is also contraindicated in those countries where
BSE is known to exist because of the risk of contamina-
tion of meat through an increased risk of neural emboli

Other methods of slaughter
Traditionally cervical dislocation has been widely used
on farm and as a backup method for slaughter in com-
mercial poultry slaughter establishment. It is not permit-
ted by current EU legislation to be used in slaughterhouses
except as a backup method and on farm only in birds
weighing less than 5 kg. It is widely considered not to
cause immediate loss of consciousness but to result in
death from asphyxiation or ischemia. There is also the
possibility that the tissue damage inflicted by the tech-
nique may be perceived by the bird as painful.
Similarly, decapitation does not result in instanta-
neous loss of brain responsiveness. Although a flat