PART THREE: METHODS OF STUNNING AND KILLING
This report deals primarily with mainstream slaughter methods,
which require animals to be stunned before they are killed.
Animals slaughtered by a religious method are exempt from
stunning requirements under UK legislation. Religious slaughter
is dealt with separately in Viva!'s 'Going
for the Kill' report.
Pre-slaughter stunning was originally introduced to protect
abattoir personnel, rather than the animals themselves. The
idea was to immobilize the animal to facilitate killing procedures.
However, the principle of stunning has now evolved to encompass
the idea that animals should be rendered unconscious before
they are killed.
UK legislation states that stunning means, 'Any process which
causes immediate loss of consciousness which lasts until death.'
The following are stunning techniques used in UK abattoirs.
How each stunning technique affects different animals will
be examined in more detail in sections four to seven.
The Captive Bolt Pistol
This stunning method is widely used for all farmed animals.
There are two types of captive bolt pistol: penetrative and
non-penetrative. Penetrative stunners drive a bolt into the
skull and cause unconsciousness both through physical brain
damage and the concussive blow to the skull. The bolt on a
non-penetrative stunner is 'mushroom-headed' and impacts on
the brain without entering the skull. Unconsciousness is caused
by the concussive blow.
The bolt is described as 'captive' because it flies out of
the barrel but remains attached to the pistol. The pistol
is placed on the centre of the animal's forehead and is either
trigger-fired or fires automatically on contact with the animal's
Percentage of plants using the captive bolt pistols (penetrative
and mushroom-headed) according to species and type of plant
Cattle (captive bolt/pith): 71.1%
Cattle (captive bolt only): 24.9%
Sheep & goats (captive bolt only): 38.3%
Sheep & goats (captive bolt/pith): 1.1%
Pigs (captive bolt): 20.5% (mainly low throughput premises)
Pigs (captive bolt/pith): 1.1%
Pithing is carried out in the majority of cattle slaughterhouses.
The practice involves inserting a wire or rod through the
hole in the head made by the captive bolt. The rod is slid
up and down to destroy the lower part of the brain and the
The Farm Animal Welfare Council say, 'From purely hygiene
considerations, the practice is not favoured. On animal welfare
grounds, provided the animal has been effectively stunned,
there is no evidence that the practice increases suffering;
by hastening brain death there may well be advantages.' (15).
NB. Pithing is due to be banned in the UK during 2001.
Studies show that this process may risk BSE infected brain
material entering the animal's carcass.
Electric head-only stunning
Electric head-only stunning with tongs is used to stun cattle,
calves, sheep, goats, pigs, rabbits and ostriches. The operator
places a pair of electric tongs on either side of the animal's
head and passes an electric current through the brain - supposedly
causing a temporary loss of consciousness.
Percentage of plants using electric head-only stunning according
to species (10) and type of plant
Sheep & goats: 56%
The RSPCA say that, 'There is increasing scientific evidence
that some animals stunned electrically using tongs regain
consciousness before they die from loss of blood.' (20) There
are two reasons for this: either insufficient electrical current
passes through the brain to stun the animal, or the time interval
between stunning and sticking exceeds 20 seconds and the animal
starts to regain consciousness.
The Scientific Veterinary Committee of the EU says that,
'Under the commercial conditions, a considerable proportion
of animals are either inadequately stunned or require a second
stun. This is mainly because of poor electrode placements,
bad electrical contacts and long stun-to-stick intervals.'
The Committee also expresses concern that, 'The strength
of electric current used should be high enough for the species
to induce a stun within one second of application. Otherwise,
the animals could suffer a potentially painful electric shock
before being stunned.'
The Welfare of Animals at Slaughter Regulations 1995 state
that electrodes should not be used to stun animals unless
the stunning apparatus incorporates a device which, 'measures
the impedance of a load and prevents operation of the apparatus
unless a current can be passed which is sufficient to render
an animal of the species being stunned unconscious until it
is dead.' (5)
In other words, electrical stunning equipment should not
be used unless a device is attached which disables the equipment
if a strong enough current cannot be achieved. This law is
being openly flouted because according to the Meat Hygiene
Service, 'such a device is not currently commercially available.'
The electric waterbath is widely used to stun chickens, turkeys,
ducks and geese. Birds are shackled upside down on a moving
conveyor which carries them to an electrified waterbath into
which their heads are supposed to be immersed. The shackles
contact a bar which is connected to earth. The strength of
the electrical current has risen in recent years - with the
aim of ensuring that birds suffer a cardiac arrest and die
when they enter the waterbath. The Meat Hygiene Service report
that in 1997/8 the average electric current applied to chickens
stunned in an electric waterbath was 157 mA. However not all
birds will suffer a cardiac arrest and scientific papers show
that there are serious flaws with the waterbath system (see
part 7: Poultry Slaughter - The Electric
Stun to kill techniques
Traditionally, animals are stunned before their throats are
cut but the stun does not actually kill the animal. Animals
die from loss of blood after their throats are cut. Stunning
techniques do not kill animals outright because it has always
been assumed that the heart needs to continue functioning
so that as much blood as possible can be pumped out of the
animal before s/he is eaten.
However in their 1984, 'Report on the Welfare of Livestock
(Red Meat Animals) at the Time of Slaughter', the Farm Animal
Welfare Council point to scientific research undertaken on
pigs at the Meat Research Institute which shows that if animals
die from a heart attack before they are knifed and bled out
there is 'no effect on the amount of blood lost, the rate
of loss or the residual content of blood in the meat.' (15)
FAWC conclude that, 'the release of blood from the animal
need not necessarily occur prior to death... and should a
change of attitude come about variations could advantageously
be made in the design and operation of stunning techniques.'
The following table shows that the number of abattoirs using
stunning methods which kill the animal outright are very low
(Source: Meat Hygiene Service Animal Welfare Survey Report,
Sheep and goats - 3.5% (7% of the national kill)
Pigs - 1.9% (not including CO2 gas stun/kill)
Chickens - 1.1% (gas stunning)
Cattle - 0.5%
CO2 Gas Stunning
Four high throughput slaughterhouses stun and then kill pigs
by exposing them to a mixture of carbon dioxide and air. The
Meat Hygiene Service say that, 'The killing of pigs by exposure
to CO2 is used in only four slaughterhouses but these premises
process 25% of the total number of pigs slaughtered each year.'
(10) 16.3 million pigs were killed in the UK in 1998, so over
4 million were stunned using CO2 gas.
The severe welfare problems associated with this stunning
technique are discussed in part 5.
Cardiac arrest stunning
Cattle, sheep, pigs, rabbits and goats can be stunned and
simultaneously given a cardiac arrest. However, as the table
above shows, very few abattoirs actually use these methods.
An electric current is either sent through the head and body
at the same time to span the brain and heart or is sent though
the head first to cause unconsciousness and then across the
chest to cause a cardiac arrest.
If administered correctly, these methods do at least remove
the risk of animals regaining consciousness while they are
bleeding to death as the heart attack should kill the animal
outright. However, the Scientific Veterinary Committee of
the EU say that when the second method is used, 'a considerable
proportion of animals are either inadequately stunned or require
a second stun. This is mainly because of poor electrode placements
and bad electrical contacts. Measures shall be taken to avoid
these practices. Otherwise, when using method 2, the animals
could suffer a potentially painful cardiac arrest.' (17)
Killing birds with gas
Researchers at the Department of Food Animal Science in Bristol
have developed gas-based techniques which can be used to stun
birds while they are still in their crates. When using this
system, birds should not be shackled and knifed until they
are dead. (21)
Viva! believes that the whole process of cramming live birds
into crates for transportation is abhorrent. But now that
this killing technique has become available, there is no excuse
for subjecting the hundreds of millions of birds who arrive
at UK abattoirs each year to the additional stress of being
unloaded, shackled up and electrically stunned before they
are killed. However, stunning with gas mixtures containing
carbon dioxide is wholly unacceptable (see below).
The following gas mixtures are permitted under UK law (5):
a) A maximum of 2% total oxygen by volume and 90% argon
(or other inert gas) by volume in atmospheric air.
b) 25% to 30% carbon dioxide by volume and 60% argon (or
other inert gas) by volume in atmospheric air.
Stunning poultry with a gas mixture does not result in an
immediate loss of consciousness. Poultry scientist Mohan Raj
says that when carbon dioxide is present in the stunning chamber,
turkeys exhibit, 'head shaking and gasping'. (22)
Carbon dioxide gas is lower in price than argon - meaning
that abattoirs could be tempted to opt for the carbon dioxide/argon
mixture rather than using 90% argon. Abattoirs should not
be placing commercial interests above animal welfare.
Sticking is the term used to describe sticking a knife into
an animal's throat or chest with the aim of causing blood
loss and brain death. When the neck is severed, the killing
is described as a 'neck stick' and when the major vessels
near the heart are severed, the killing is described as a
'thoracic stick'. After being stuck, an animal's blood pressure
is supposed to fall quickly, resulting in a rapid loss of
blood supply to the brain. If the major blood vessels are
adequately cut, animals should lose between 40 and 60% of
their total blood volume. (23)
Researcher Steve Wotton explains that, 'Poor sticking, leading
to inadequate or delayed exsanguination, can allow blood pressure
to be maintained so that sensibility is regained before death
In order to ensure that animals are not recovering from a
stun, slaughtermen are supposed to check that animals have
an absence of rhythmic breathing movements and an absence
of a corneal (eye) reflex.