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Mechanical, electrical or gas stunning; slaughter methods and monitoring signs of unconsciousness or consciousness

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Introduction: pre-slaughter stunning

The outcome of stunning prior to slaughter is to render the animal unconscious such that it is insensible to any pain and distress associated with the cutting and bleeding out slaughter activity. Despite this beneficial outcome of avoidable suffering and pain, nevertheless, stunning is a universally recognized slaughter activity that carries a substantial animal welfare risk. Not only can the stunning method itself cause suffering if ineffectively done, it can result in the completely unacceptable situation where a still conscious animal is exposed to further dressing procedures that will cause it great anguish before it dies.

Stunning methods may be irreversible which means the animal will not regain consciousness although the heart may still be beating. By contrast, reversible stunning methods will allow the animal to regain consciousness and these rely on the bleeding out stage from cutting the blood vessels to result in the death of the animal.

Stunning should fulfill the following requirements in order to demonstrate the outcome of avoidable suffering to the individual food animal:

Assessing the state of unconsciousness in the stunned animal is not always a straightforward task. The definitely conscious will be clearly distinguishable from the definitely unconsciousness (including brain dead) by observation of well documented signs associated with these states. However there is a transition zone or a gray zone between consciousness and unconsciousness when the animal may slide into and out of consciousness that may require re-stunning the animal to avoid a return to consciousness.

There is the risk for any stunning method to fail; however with well trained and qualified staff, equipment used according to the manufacturer's specifications and which is always kept well maintained, these risks should be controllable to the point that the outcome of avoidable suffering can be achieved.


For the purposes of this document, the following definitions apply:

Alternating current (AC)
Flow of current that varies cyclically in direction and Magnitude (Courant alternatif - CA)
Equipment for measuring current flow (Amps) (Ampèremètre)
The strength of an electric current expressed in amperes (Intensité)
Amperes (Amp)
The unit used to measure the flow of current (Ampère)
Backup stunning equipment
Stunning equipment kept ready and available for use, if primary equipment fails to operate properly (Équipement d'étourdissement d'urgence)
Bleeding out
The act of causing blood loss sufficient to result in death (Saigner)
Bleed-out time
The time it takes to cause sufficient blood loss for sticking to result in death (Temps de la saignée)
Clonic seizure
A seizure characterized by a succession of convulsive spasms (Attaque clonique)
The rate at which the charge is flowing (Courant)
Direct current (DC)
Current that flows constantly in only one direction (Courant continu - CC)
Dead on arrival. (MA - Mort à l'arrivée)
Dressing or dressing procedure
Any cutting or removal of a body part, with the exception of an incision made for bleed out (Procédure d'habillage)
The use of electric current to immobilize animals – which should not be confused with electric stunning; immobilized animals are paralyzed but sensible (Électro-immobilisation)
Insensibility achieved by stunning with electricity (Électronarcose)
Establishment licence holder
The licence holder or legal entity issued a licence to conduct slaughter activities in an establishment that slaughters animals for food (Titulaire de licence d'établissement)
Draining the body of blood (see "Sticking" or "Bleeding out") (Exsanguination)
Frequency (related to electricity)
How many times, in a set time frame a cycle is repeated (Fréquence)
Head-only stunning
Stunning with electric current applied across the head. This type of stun is short lived, animals recover rapidly, if not bled out immediately (Étourdissement tête seulement)
Head-to-heart stunning
Stunning where the current spans the brain and heart simultaneously, or spans the brain and immediately thereafter the heart. This type of stun is sometimes called "irreversible electric stun." (Étourdissement tête-cœur)
High frequency
Cycles of electricity, greater than 200 Hertz (Hz), used to stun animals (Haute fréquence)
Hot wanding
A painful pre-shock received by animals (usually hogs) being stunned with electricity, if current flows before the electrode (wand) has made full contact with the animal. Animals, in general, that have been hot wanded will vocalize when the wand is applied (Chocs électriques prématurés)
A state of unawareness in which there is a temporary or permanent disruption of brain function, as a result the animal is unable to respond to normal stimuli, including pain.(used interchangeably with "unconscious") (Insensible)
Low Frequency
Cycles of electricity, between 50 to 200 Hertz (Hz) used to stun animals (Basse fréquence)
Ohms Law
Current (Ampere or Miliampere) = Voltage (Volts) ÷ Resistance (Ω = Ohms)
Penetrative stunning
Stunning where the device, such as a captive bolt gun, penetrates the skull (Étourdissement pénétrant)
When a projectile (from a firearm) exits the skull on the opposite side from which it entered (Perforation)
Pre-stun pen
A pen near the stunning area used to hold animals prior to slaughter (Enclos de pré- étourdissement)
Properties that limit current flow (related to electricity) (Résistance)
Restraint conveyor
A moving conveyor that holds an animal in the correct position for accurate stunning (Convoyeur de contention)
Rhythmic breathing
A regular breathing pattern, indicating (at least partial) brain stem function; generally characterized by two or more inspiratory and expiratory cycles of the thorax (Respiration rythmique)
When a projectile (from a firearm) rebounds off a surface (Ricochet)
A state of awareness where there is an ability to respond to stimuli, including pain. Sensibility requires function of the brain stem and some cortical regions of the brain. Used interchangeably with "consciousness" (Sensibilité)
The cutting of major blood vessels to allow bleeding out (Saignée)
Stun box (knocking box)
A small enclosure in which individual animals are confined for stunning (Boîte d'assommage)
Stunning pen
A pen where animals are stunned, usually in small groups (for example, lambs, pigs) (Enclos d'étourdissement)
Stun-to-stick interval
The time between an animal being rendered unconscious by stunning and the time that the major blood vessels are cut (Intervalle entre l'étourdissement et la saignée)
Tonic seizure
Seizure characterized by rigid muscle tension immediately following an electrical or mechanical stun. (Crise tonique)
A state of unawareness in which there is a temporary or permanent disruption of brain function, as a result the animal is unable to respond to normal stimuli, including pain (Used interchangeably with "insensible") (Inconscient)
Is the difference in charge between two points (Tension)

Mechanical stunning of food animals

Captive bolt stunning

Penetrative captive bolt stunning

Non-penetrating captive bolt stunning

Preventive Control Plan (PCP) for captive bolt equipment

Firearm stunning

Captive bolt stunning of poultry or rabbits

Electrical stunning

Electrical stunning methods for mammalian food animals

Electrical stunning systems for poultry

Electrical multiple bird stunning systems for poultry

Animal welfare PCP for electrical multiple bird stunning of poultry

The licence holder's PCP should include the following preventive measures, procedures and information:

Electrical stunning of poultry and ratites head-only stunning, hand-held or automated equipment (poultry)

Undersized birds
Pre-stun shocks

Controlled atmospheric stunning (CAS)



Design of facilities for CAS of pigs

Animal welfare PCP for gas stunning for pigs

CAS of poultry

Low atmospheric pressure stunning (LAPS)

Decapitation of poultry as a deviation procedure for missed stuns in poultry

Monitoring for signs of consciousness (sensibility) and unconsciousness (insensibility) in food animals after stunning

Table of signs for monitoring the outcome of stunning in mammalian food animals
Signs Neurophysiology of sign How to evaluate
loss of posture
  • a functioning reticular formation is required for the standing posture and is affected by all forms of stunning
  • Collapse occurs immediately after effective mechanical and electrical stunning
  • However, collapse can also be caused if the mechanical penetrative or electrical device is improperly place on the neck, bypassing the brain and resulting in immobilization or paralysis without unconsciousness
  • Gas stunning results in the gradual loss of the ability to stand
spontaneous blinking
  • blinking is generated by an eye preservation reflex
  • absence of blinking indicates the required cranial nerves have lost sensory and motor function
  • involves circuits in the brainstem and cortex
  • monitoring for spontaneous blinking is a useful indicator of consciousness
  • spontaneous blinking must be absent after effective stunning
  • repeated spontaneous blinking can be a sign of consciousness, especially if occurring together with eye movements, focused on external stimuli
wide open relaxed eye and pupil
  • the nerves innervating the eyeball and pupil are non-functional
  • indicative that brain activity is impaired
  • a wide open, relaxed eye with a blank stare can be taken as a good indicator of unconsciousness
  • wide open, relaxed eyes and pupil can indicate a dead animal

eye reflexes:

  • corneal reflex
  • palpebral reflex
  • corneal reflex and palpebral reflex have similar neural circuits but palpebral disappears first
  • absence indicates a loss of brain stem function and thus loss of sensibility
  • do not use corneal reflex to evaluate efficacy of electric stunning because of tonic seizure activity which may affect eyeball muscles
  • can be taken as a sign that the brain is reorganizing after stunning
  • absence of corneal reflex is a reliable indicator of unconsciousness


  • vertical or horizontal rapid oscillation of the eyeball or 'vibrating eye'
  • presence of nystagmus suggests dysfunction in the underlying circuits of the brain or damage to the cerebellum of vestibular system
  • the implication of nystagmus depends on the stunning method used
  • nystagmus is often seen during seizure caused by effective electrical stunning in all species, especially at higher frequencies
  • if nystagmus occurs after captive bolt stunning this is generally associated with an ineffective stun and requires a restun
tracking or eye pursuit movements
  • involves cortical and brainstem activity
  • if intentional eye movements are present, the animal is conscious

threat test or menace reflex

  • involves higher-order cortical activity in perception and integration of information from the environment
  • hand or finger movement towards the eyes and a blinking or withdrawal reaction indicates animal is conscious
eyeball rotation
  • eyeball movement depends on muscles that receive information from brainstem, which is controlled by higher brain centres
  • full or partial eyeball rotation after mechanical stunning in cattle indicates a risk of return to consciousness and requires a second stun

rhythmic breathing

  • ribs move in and out at least twice

gasping (agonal)

  • intermittent forceful and disorganized inspiratory movements
  • rhythmic breathing is coordinated by the brainstem (medulla oblongata) and through information received from the periphery and higher brain centres
  • agonal gasping can be induced by ischemia or hypoxia and precedes death
  • absence of rhythmic breathing is consistent with unconsciousness or death
  • presence of breathing is a sign of return to sensibility after all methods of stunning
  • it is a prime indicator of poor stunning
  • check the flank, nostril and mouth for signs of rhythmic breathing
  • gasping may be observed after effective electrical or gas stunning but should not occur after effective mechanical stunning
  • agonal gasping resembles the gasping movements of 'a fish out of water'
  • when the breathing reflex starts to return, it can begin as regular gagging until recovery of rhythmic breathing
  • requires function of somatosensory and motor cortex
  • intentional vocalization indicates consciousness
  • when it occurs with stunning, is a pain response
  • gasping accompanied by guttural sounds are not the same as vocalization
limb movements
  • kicking or paddling after stunning is most often a sign that inhibition of spinal nerve transmission patterns is lost
  • they are involuntary moments that are independent of consciousness
  • in addition, the somatic reflex arc may sometimes cause the unconscious animal after stunning to react to sticking/cutting painful stimuli, usually in the form of movement of the forelegs; these are spinal reflexes that do not involve the central nervous system
  • paddling of limbs can occur in unconscious animals during gas stunning but the body is limp
  • tonic seizures post-stunning are characterized by an arched back and rigidly flexed legs under the body; these are expected signs for mechanical and electrical stunning and are followed by clonic seizure activity that includes random leg kicking or paddling
  • evaluate with other signs and type of stunning method
righting/ arched back
  • righting reflex may be helped by subcortical CNS structures, but in most cases means function of the cerebral cortex and return of proprioception and muscle tone
  • righting may be impaired by shackling or restraint or the use of certain current forms in electrical stunning
  • an animal attempting to right itself will have an arched back, and attempt to raise its head or attempt to regain posture
  • if the righting reflex is present it is very likely that the animal is sensible
  • a relaxed tail does not occur together with an arched back or righting
  • body hangs straight down except sheep with neck hanging at an angle because of different anatomy
floppy head
  • a floppy, flaccid, relaxed head and neck, hanging straight down in shackled animals indicates that muscle tone and in most cases cerebral control over posture are lost
  • if the head is floppy, in most cases consciousness is lost
tension in the nose , upper lip and curled tongue
  • muscle tension in the jaw, mouth or lips can indicate presence of cranial nerve function (sign of returning to sensibility)
  • these signs can be useful indicators of poor stunning particularly in animals that are stunned with a captive bolt (less useful with firearm, electrical or gas stunning )
response to painful stimulus
  • response to nose prick or pinch or ear pinch may indicate presence of cortical nerve activity in the respective circuit of sensory and motor cranial nerves
  • other responses may be a simple nociceptive arc-reflex response, based on a neural circuit that passes through the spinal cord, but not the brain
  • the nerves involved in the arc-reflex retain some functionality for a while after unconsciousness
  • response to nose prick/ear pinch may indicate consciousness or possible return to sensibility
  • ventral movement of neck in response to cutting of skin and blood vessels can be a nociceptive reflex response involving the spinal cord only; the reaction to the skin cut and other tissues cannot be used as an indicator of consciousness
  • need to evaluate with other signs, such as whether the head is floppy
tongue hanging out
  • a relaxed tongue may indicate loss of cranial nerve function
  • The tongue may hang out also due to gravity when the jaw muscles are relaxed, and this is a sign that the animal is unconscious
  • This can be confirmed by manipulating the jaws by hand and if there is no resistance to movement, the animal is unconscious
  • A curled tongue can be a sign of possible return to sensibility
Table of signs for monitoring the outcome of stunning in avian food animals
Signs of unconsciousness Signs of consciousness or return to consciousness
  • neck positions are variable but should be consistent for all birds in a lot using same electrical parameters
  • for example the necks will be initially stiff and arched (perhaps parallel to the ground when shackled); this phase will rapidly disappear after neck cutting so applies to step between stunning neck cutting
  • then the head and neck will become limp after the clonic seizure phase is finished; flaccid head
  • absence of rhythmic breathing (check cloaca for movements to indicate breathing)
  • absence of spontaneous blinking and the third eyelid (nictitating membrane) reflex
  • absence of other eye reflexes (palpebral, corneal and pupillary)
  • eyes open and fixed
  • initial tonic phase of the seizure includes:
    • constant rapid body and wing tremors immediately after stunning
    • wings held tightly against the body
    • rigidly extended legs (may be difficult to see in shackles)
  • clonic phase of the seizure includes:
    • may have petit mal body convulsions including non-intentional wing flapping after rapid body tremors have stopped
  • presence of vocalization
  • rhythmic breathing (check cloaca for movements to indicate breathing)
  • absence of tonic/clonic seizures
  • swallowing reflex (deglutition reflex), manifested as beak movements after stunning (from water entering mouth) and after cutting (from blood entering the mouth)
  • spontaneous blinking (third eyelid)
  • shaking of head during cutting and bleeding from blood entering nares (intentional body movement)
  • vigorous wing flapping (intentional body movement)
  • return of tension in the neck after the limp phase
  • righting reflex
  • some types of current systems can have a relaxing or immobilizing effect on the neck ; in these cases the signs of return to sensibility after stunning can be masked
  • response to pain, such as neck cutting, can be an arc-reflex involving spinal neural pathways only and is not a reliable indicator for sensibility; it must evaluated with other signs and what electrical parameters are used to stun the bird
Captive bolt
  • loss of posture
  • loss of rhythmic breathing (check cloaca for movement to indicate rhythmic breathing)
  • tonic seizures
    • rigidly extended legs (more difficult to see when shackled)
    • wings are held tightly against the body
    • constant rapid body tremors
    • arched neck
  • clonic seizures:
    • vigorous involuntary flapping and severe convulsions
  • absence of a third eyelid (nictitating membrane) movement and other eye movements and reflexes
  • rhythmic breathing
  • swallowing
  • blinking (third eyelid)
  • intentional body movements
  • righting reflex
  • response to pain, such as neck cutting can be an arc-reflex involving spinal neural pathways only is not a reliable indicator for sensibility; it must evaluated with other signs, such as whether the head is floppy
Gas Stunning (Controlled Atmospheric Stunning)
  • loss of posture, muscle tone, relaxed, limp body
  • no rhythmic breathing (check cloaca for movement to indicate rhythmic breathing)
  • absence of third eyelid (nictitating membrane) reflex or spontaneous blinking
  • wings drooping
  • absence of vocalization
  • rhythmic breathing
  • swallowing
  • blinking (third eyelid) and third eyelid reflex
  • wings not drooping / body movements
  • righting reflex
  • vocalization

Cutting and bleeding methods for conventional slaughter

Cutting/bleeding of red meat species including ratites

Cutting/bleeding of rabbits

Cutting/bleeding of poultry

Uncut red birds and inadequately bled birds


CFIA Regulatory requirements for humane treatment of food animals during slaughtering activities under the Safe Food for Canadians:

CFIA guidelines of best practices:

Controlled atmospheric stunning (CAS) references:

Electrical stunning references:

General references for stunning and slaughter of food animals:

Monitoring of stunning references:

References for physiology of stunning and signs of consciousness/unconsciousness:

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