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