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

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:

• The animal should remain in a state of unconsciousness that extends beyond the time required to use a neck cut to bleed the animal that results in death
• The stunning method should result in minimal signs of distress in the animal before the loss of consciousness

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.

Definitions

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)

Ammeter

Equipment for measuring current flow (Amps) (Ampèremètre)

Amperage

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)

Current

The rate at which the charge is flowing (Courant)

Direct current (DC)

Current that flows constantly in only one direction (Courant continu - CC)

DOA

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)

Electroimmobilization

The use of electric current to immobilize animals – which should not be confused with electric stunning; immobilized animals are paralyzed but sensible (Électro-immobilisation)

Electronarcosis

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)

Exsanguination

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)

Insensible

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)

Perforation

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)

Resistance

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)

Ricochet

When a projectile (from a firearm) rebounds off a surface (Ricochet)

Sensibility

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)

Sticking

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)

Unconscious

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)

Voltage

Is the difference in charge between two points (Tension)

Mechanical stunning of food animals

• the outcome of mechanical stunning produces a pathological state of the brain incompatible with consciousness and sensibility until the animal can be bled out
• mechanical stunning requires proper targeting to achieve this outcome
• the best landmark for the targeted area is a midline frontal approach
• the projectile, when used, should be targeted towards the animal's brainstem for most consistent stunning results
  • targeting the brainstem using landmarks other than midline frontal may include, for example,:
    • the side of the head, behind the ear or near the poll at the top or the back of the head
• however, alternative approaches may increase the likelihood that the brainstem and midbrain will be missed
• a projectile can sever the spinal cord without causing unconsciousness
• If a landmark other than the midline frontal is used then it will require documented evidence or validation by the licence holder to show the alternative approach can stun the animal properly:
  • for example, a poll (top of the head) entry using firearms may be more useful for heavily horned sheep and all goats

Captive bolt stunning

• captive bolt stunning may be penetrative or non-penetrative
• both methods rely on the outcome of instantaneous and massive disruption of brain function to render the animal unconscious
• Cartridges with compressed air, gunpowder or a spring under tension drive the bolt either against the skull or through it

Penetrative captive bolt stunning

• the outcome causes unconsciousness from the combined effect of the concussive blow to the head and the penetrating bolt creating damage to the brain as it passes through and retracts
  • the impact alone creates pressure or shock waves that have multiple effects disrupting normal brain function, including flattening of the cerebrum contralateral to the shot
  • the passage and retraction of the bolt creates additional damage from a cavitation effect, hemorrhage, bone fragmentation, crushing, laceration and tearing of axons and blood vessels
• even when the targeting is not optimal, such as when the animal moves, the animal may still be correctly stunned because of the massive damage from the impact and local damage of the bolt; therefore, slightly lower or slightly higher targeting can still work as long as essential parts of the brainstem are still damaged
• however if the relevant structures are not damaged or the damage is limited, the animal may be still conscious or partially conscious and will require a second stun
  • targeting too high will only reach the cerebellum
  • targeting too low will only slightly damage the frontal cortex with the undesirable outcome that the animal is wounded but conscious

Non-penetrating captive bolt stunning

• the outcome relies on the mushroom head causing unconsciousness from the concussive impact of the blow alone
• rapid oscillations in the resulting pressure waves cause the resulting loss of consciousness
• there may also be concurrent fracturing of the skull from the impact and internal brain hemorrhage
• it requires extreme accuracy to be effective; therefore the landmarks are extremely important
• for this reason, it should be used only in very young and small animals such as poultry, rabbits, and ruminants weighing less than 10kg and the head should be well-restrained to help with the accuracy of the blow
  • However, in immature animals, this method may crush the skull and result in an ineffective stun

Preventive Control Plan (PCP) for captive bolt equipment

• The licence holder's written animal welfare PCP for the captive bolt stunning equipment should include the following preventive measures, procedures and information:
• equipment operators are trained and competent to use the equipment and are able to monitor the signs of an effective stun for each animal
• the design, caliber, charge, bolt length, bolt tip, and bolt velocity are:
  • appropriate for the type of animal, as per the manufacturer's directions and/or specifications
  • effective for the licence holder's intended use
  • documented in the written PCP
• there are a sufficient number of equipment so they can be rotated to prevent overheating, and can be available as a backup stunning method
• equipment is used, cleaned, and maintained, and stored as per the manufacturer's recommendations
• charge cartridges are stored in a clean dry area and have not aged excessively
• bolt velocity is checked by a velocity checker, or similar means as stated in the manufacturer's directions
• bolt(s) retract completely, as designed, after each use
• the procedure including test equipment and frequency for testing the stunning equipment
  • it is never tested on a live animal
  • frequency should include at a minimum at the startup of production, production shift changes, before each new lot of birds or employee shift changes

Firearm stunning

• Firearm stunning is used only when the:
  • licence holder has demonstrated that no other means of stunning is practical or works as well:
    • for example, for horses, firearms may give a better stun than captive bolt stunning, depending on stun pen layout, horse temperament and nature
  • equipment operators are trained and competent to use the equipment and recognize the signs of an effective stun
  • caliber and range are suitable for the species and class of animal
  • the ammunition selected for the species and body type to be slaughtered provides effective stunning while minimizing over-penetration or the effects of misdirected bullets or ricochet
  • ammunition is stored in a clean dry area and has not aged excessively
  • the firearm is cleaned and maintained and stored to ensure it functions effectively
• In addition, there should be:
  • a bullet proof barrier between the stunning area and the kill floor to protect people from the effects of misdirected bullets, slugs, or ricochet
  • remote viewing to allow monitoring of stun efficacy and bleed-rail insensibility with protection from the effects of misdirected bullets or ricochet
  • a visible warning system to indicate when firearms are being discharged
  • back-up stunning equipment, readily available
• The licence holder's written PCP should include:
  • written documentation that the equipment complies with the federal Firearms Act and all applicable provincial and local legislation and that firearms are well maintained as per manufacturer's recommendations
  • equipment operators are trained and competent to use the equipment and are able to monitor the signs of an effective stun for each animal
  • the procedure including test equipment and frequency for testing the stunning equipment
    • it is never tested on a live animal
    • frequency should include at a minimum at the startup of production, production shift changes, before each new lot of birds or employee shift changes

Captive bolt stunning of poultry or rabbits

• This method of stunning:
  • can be used as the primary method of stunning birds or rabbits in low volume establishments because of the slower line speeds
  • requires equipment appropriate for the species
  • is performed by competent personnel as per the licence holder's animal welfare PCP:
    • equipment operators are trained and competent to use the equipment and are able to monitor the signs of an effective stun for each animal
    • the procedure including test equipment and frequency for testing the stunning equipment
      • it is never tested on a live animal
      • frequency should include at a minimum at the startup of production, production shift changes, before each new lot of birds or rabbits or employee shift changes

Electrical stunning

• The outcome of electrical stunning is to pass current of sufficient strength and duration through the brain to interrupt normal brain rhythmic electrical activity.
• If done correctly, the circuit from electrifying the electrodes will produce an electric field in the brain that depolarizes or hyperpolarizes the neuronal membranes resulting in an epileptiform seizure, which renders the animal unconscious.
• Depending on which areas of the brain are affected, this state of unconscious can be superficial and short lasting or deeper and longer lasting.
• When the current passes through heart as well, either simultaneously or sequentially, this can cause cardiac fibrillation with subsequent cardiac arrest and death.
• Head-only stunning requires that electrified electrodes span the brain so that the circuit will pass through the brain
• Head-body stunning for mammals requires that two electrified electrodes span the brain and a third one is on the chest, sternum or back
• Head-body stunning for poultry is usually accomplished through a multiple bird electrical waterbath system; however this is very dependent on the electrical parameters used for the system
• The threshold current necessary to induce immediate loss of consciousness for effective stunning is more than that required to produce seizures or loss of muscular reflexes as occurs with electroimmobilization:
  • electroimmobilization without loss of consciousness can result in avoidable suffering to the animal
  • Animals that are electroimmobilized look virtually the same as those that are effectively stunned.
  • Animals that are electroimmobilized are still conscious and sensible to stimuli, including pain stimuli
  • Therefore electrical stunning parameters should be used that can induce epileptiform seizure activity in the brain

Electrical stunning methods for mammalian food animals

• Electrical stunning includes hand-held and automated electrical stunning equipment.
• Correct use of this equipment includes:
  • the right equipment is used for the right species at all times
  • the current (amperage and voltage) is adequate for the species slaughtered to avoid electroimmobilization
  • employees who conduct the stunning require adequate training for the specific equipment used
  • animals are well restrained and stay calm
  • for head-only stunning, the outcome is a reversible stun
  • the electrodes must always be placed to span the brain for the current to flow properly through the brain for all food animals
    • therefore, the electrode(s) are not positioned on the animal's neck or muzzle, for example for rabbits:
      • when electrical head-only stunning equipment for rabbits is used to make contact with the muzzle of the rabbit and not span the brain, this will cause electroimmobilization only and not an effective stun
    • for head only electric stunning, the stun-to-stick interval should not exceed 15 seconds for most species
  • for head-to-body stunning, the outcome is generally an irreversible outcome, when done properly
  • incidents of preshock or electroimmobilization are to be monitored to prevent avoidable suffering:
    • hot wanding occurs if an animal receives a cardiac shock before they receive a head stun
    • preshocked animals will generally vocalize because of the pain (except for sheep)
• The licence holder's written PCP should include the following preventive measures, procedures and information:
  • the stunning equipment is clearly defined which type of stunning it is meant to provide , including reversible or irreversible stunning outcome
  • the protocol requiring that it is used properly as per the manufacturer's specifications to result in an effective stun
    • the equipment is positioned correctly to span the brain for the current to flow through the brain
  • there is a written protocol for the routine maintenance of the equipment
  • the procedure including test equipment and frequency for testing the stunning equipment
    • it is never tested on a live animal
    • frequency should include at a minimum at the startup of production, production shift changes, before each new lot of animals or employee shift changes
  • the recommended equipment settings for each size of animal that is stunned including specification of:
    • the voltage
    • amperage
    • the current frequency
    • type of current (AC vs DC or both)
    • type of wave form (sinus, square)
    • the time of stun
  • In cases where the manufacturer's recommendations are not used, there should be documented evidence or a validation study in the establishment to support the alternative approach
  • the voltage and amperage are monitored, easy to see and are recorded on an ongoing basis throughout the shift
  • the amperage is the more important parameter to assess effective stunning
  • the length of time of the current is applied on the animal is measured and recorded
  • a backup and well maintained stunning equipment should be quickly available as a deviation procedure

Electrical stunning systems for poultry

Electrical multiple bird stunning systems for poultry

• Waterbath and plate stunners are available as single phase or multiphase systems:
  • either only one electrical phase of one waveform and current amplitude is used, or two phases of differing waveforms and/or current amplitudes are used consecutively:
    • For example, for a two plate, two phase system:
      • one phase delivers an AC (lower frequency alternate current phase, with sinusoidal waveform) current and the other delivers a DC pulsed current (higher frequency, direct pulsating current phase)
      • each phase section (AC and DC) should be equipped with meters to measure the amount of current, as well as voltage, being supplied to that section of the stunner to assess the effective functioning of the equipment
      • the calculations of the amount of current being provided to stun each bird is not the sum of the amount delivered to each phase since each section is a separate stunning phase of the entire system and the amount delivered to each bird depends on the number of birds in each stunning phase at one time
      • each phase section (AC and DC) should be supplied with sufficient current to render the bird insensible, otherwise there is a risk of ineffective stunning or electroimmobilization
      • the ground bar should come in contact with all shackles over the AC and DC phase sections
    • For example for a single phase waterbath system:
      • the height of the waterbath stunner water level and the level of brine in the waterbath stunner are adjusted throughout the day as needed to ensure even the smallest birds are submerged up to the base of their wings, or the birds' shoulders in the electrified water
      • For systems requiring increased salinity, salt can be added to the waterbath solution before the stunning starts and an effective salt concentration of the brine is maintained throughout the day to facilitate the flow of an effective electric current through the birds
      • Both AC or DC currents are used in single phase water bath systems with either sinusoidal or square waveforms
      • lower frequencies at higher amperages and voltages produce more effective and longer stunning times in the birds
    • For example for a single phase plate (grid) stunner:
      • For the electrical current to flow properly to the brain, the plate should make contact with the eye of the bird (side of the head)
      • When using high enough voltages, they can be effective for head-only stunning
      • most electric plate stunners are designed to have a brine solution that just covers the electric plate (wet plate)
• Effective stunning is highly dependent on the voltage and especially the current amperage used:
  • poultry are electrically stunned using sufficiently high current, voltage and length of application, the stun could become irreversible and result in the bird's death
  • when using lower voltages for electric wet plate stunners, there can be a higher inherent risk of electroimmobilization or ineffective stunning
  • in general, the higher the frequency and the lower the voltage and current amperage, the more likely the bird will return to sensibility rapidly and the higher the risk for birds that could be electroimmobilized
  • theoretically, the current flowing through each bird is dependent on the total amperage of current, the number of birds and the amount of resistance in each bird
  • in practice, divide the total current flow registered on the ammeters by the number of birds in the bath to get an approximate idea of current amperage per bird
    • Note that even with low frequency, high current systems, the bird may recover to some degree if the current is not delivered properly to the individual bird.
      • Some reasons for this include higher resistance from an individual bird or the bird's incorrect positioning when presented to the source of electricity.
    • Electroimmobilization may occur if the current bypasses the brain in the multiple bird electrical waterbath or plate systems.
      • For example, this can occur if a bird swan necks and another body part makes contact with the electrified waterbath first for electrical waterbath stunners and therefore the brain is bypassed with no resulting epileptic seizure.
• For all multiple bird systems, birds should only be suspended on the shackle line for a minimum amount of time, not more than 2 minutes for ducks, geese and turkeys and not more than 1 minute for other poultry prior to stunning because:
  • they have no diaphragms and there is increased cardiac pressure and bird death when in a prolonged inverted position
  • furthermore, there is the risk of pain and injury from the shackle from compression on the metatarsus, especially if it is not the correct size slot for the size of bird
    • shackles with moveable, tapering slots generally work better than parallel slots
    • if the shackles are too large there will be poor contact and insufficient current flow
    • if the shackles are too small it will be painful and induce flapping which interferes with stunning
    • wetting shackles can improve conductivity
• The output of the electrical equipment (volts or amps) should be tested under load, using equipment which can simulate the resistance of a shackled bird or a bird's head depending on the placement of the electrodes
• the waterbath should be sufficiently large (width, length and depth) to accommodate the wing span and body mass for the type of bird(s) being slaughtered and to avoid birds heads or other parts being trapped outside of the waterbath sides
• all equipment should be cleaned, maintained, adjusted and tested to ensure it is operating properly with good current flow before the beginning of each day's operations
• the water bath (live) electrode needs to be kept clean and must run the entire length of the waterbath to facilitate current flow
• the ground (shackle) electrode needs to be regularly cleaned and have constant contact with the shackles since intermittent contact results in a less effective, intermittent stun

Animal welfare PCP for electrical multiple bird stunning of poultry

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

• protocol for the maintenance of the stunning equipment
• methods used to determine the electrical settings for each lot and type of birds processed, including a means to validate effective stunning parameters
• the recommended equipment settings for each size of bird that is stunned including specification of:
  • the frequency of current (AC/DC) and which one is used for which step
  • the time of stun (taking into account the line speed and length of the stunner)
  • number of birds stunned at the same time and for each step in a two-phase system
  • the protocol for the maintenance of the equipment for salinity flow
  • the protocol for level of salinity used and its adjustment including:
    • manufacturers recommended procedures to enhance the salinity of water to improve electrical conductivity, as required
  • correct flow of the brine to avoid preshock from the brine flowing out the entrance to the bath
  • maintenance and cleaning protocol of shackles for electric contact to prevent poor electrical conductivity
  • the protocol for staff for stopping the line in the stunning and bleeding areas in the event of a problem or communicating problems so that corrective action procedures can be immediately taken
  • the system used should have meters or the proper software if computerized that display or record the amperage (ammeter) and/or volts (voltmeter), frequency and duration of the stun
  • meters (voltmeters and ammeters) are best installed where clearly visible to staff operating the electrical water bath or plate stunning systems and to any person who monitors, verifies, inspects or audits the system
• the procedure including test equipment and frequency for testing the stunning equipment
  • it is never tested on a live animal
  • frequency should include at a minimum at the startup of production, production shift, before each new lot of birds or employee shift changes

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

• Electrical head-only stunning includes hand-held and automated electrical stunning equipment.
• The electrodes, whether hand-held or automated (multiple bird systems) must still span the brain to produce an effective stun
• Equipment that is designed for a single point contact with the head or neck (for example, an electric knife) may not produce an effective stun; there is the risk that it will only immobilize (paralyze) the bird without inducing unconsciousness.
• For ratites (emus, rheas and ostriches), if hooded, this will require increased amperage for an effective stun
• The licence holder's PCP should include the following preventive measures, procedures and information:
  • the recommended equipment settings for each size of bird that is stunned including specification of:
    • the voltage
    • amperage
    • the current frequency
    • the time of stun
    • a means/protocol to validate effective stunning parameters
    • the electrical stunning equipment is maintained and cleaned, as stated in the licence holder's written PCP and the manufacturer's specifications
    • in cases where the manufacturer's recommendations are not used, documentation to explain the rationale for the alternate approach should be developed and maintained
    • the voltage and amperage are monitored and recorded throughout the shift
    • the length of time of the current is applied is measured
  • safeguards that the equipment does not deliver any shock before stunning occurs
    • requirements that the electrodes are always positioned to span the brain and never on the bird's neck or beak
  • requirements that the stun-to-stick interval should not exceed 15 seconds
  • requirements for a backup stunning equipment to be available and properly functional
  • the procedure including test equipment and frequency for testing the stunning equipment
    • it is never tested on a live animal
    • frequency should include at a minimum at the startup of production, production shift, before each new lot of birds or employee shift changes

Undersized birds

• undersized birds should not be hung, unless they can be effectively stunned by the water bath with the proper adjustments of the equipment
• these undersized birds or runts should be humanely killed by an appropriate method if they cannot be effectively stunned

Pre-stun shocks

• Pre-stun shocks should be monitored and prevented since it is painful for the birds and the licence holder should take the necessary steps to prevent it, including the determination of the root cause.
• Pre-stun shock occurs when any part of a bird receives an electric shock before it enters the waterbath or in other cases, before it is effectively stunned.
• Examples of these other cases include, the brine level being too low or the bird being too small to contact the water properly.
• A ramp at the entry to the waterbath or plate system with water should be sloped to swing the birds into the waterbath
• The ramp should also be either insulated or isolated by inserting a layer of non-conducting material (in the form of sheets or rods) between the ramp and the birds to avoid the birds making direct contact with any electrified water on the ramp

Controlled atmospheric stunning (CAS)

• CAS stunning in Canadian federal slaughter facilities, using CO₂, is used for pigs and poultry to stun (reversible) or kill (irreversible) prior to bleeding, depending on concentration of the gases used and duration of exposure to them.
• CAS systems using CO₂ with air or O₂ result in the inhibition of the neurones with the outcome of a progressive loss of consciousness
• CO₂ rich mixtures induce hypercapnia and hypoxia
• The resulting acidification inhibits neuronal activity and produces an anaesthetic like effect

Pigs

• For current systems in use in North America, pigs are exposed to induction levels of high concentrations of CO₂ with air.
• Some pigs react to the gas at these high concentrations by attempting to escape and showing marked shaking of their heads.
• The CO₂ may cause the observed behaviour because of its direct irritating effect on the mucous membranes
• Pigs can also exhibit gasping type of breathing or hyperventilation during induction but this may be more due to a brainstem response to the hypercapnia rather than a sign of aversive behaviour.
• While mild signs of response to the irritating effects of the gas are not uncommon, genetics and breeds of the pigs may play a role in the degree of the pig's reaction to the high levels of CO₂.
• For this reason, the pigs should be monitored before they demonstrate loss of posture for any signs of extreme aversive behaviour, such as escape behaviour and corrective action measures implemented, such as adjusting gas concentrations.

Poultry

• For poultry, there is the advantage that the birds can be stunned in the transport containers if they are specially designed modules for this purpose and therefore, the birds are minimally handled while still conscious.
  • However, it may not always provide a consistent uniform stunning concentration of CO₂ to each bird
  • This may lead to a failure to stun some birds or that some birds regain consciousness prior to bleeding
• For some systems in use, a more gradual increase in CO₂ is carried out in multiple steps, starting with lower levels during induction, reaching a maximum effective level of CO_2, depending on class or species of poultry, average weight of birds and equipment.
• Another approach is to mix O₂ with the CO_2, during the induction phase, and then gradually reduce the O_2, while increasing the CO₂ to a maximum effective level
• Total dwell time will depend on class or species of poultry, average weight of birds, equipment and parameters used and whether the outcome is intended to be reversible or irreversible stunning.

Design of facilities for CAS of pigs

• The pre-stun facilities in lairage, including gondolas and automated gates to move the pigs, and the stunning chambers, pit, in addition to the post-stun facilities, should be specifically designed:
  • for CAS stunning and for the size and weight of pigs
  • to avoid injury, overcrowding or unnecessary stress
  • to continuously measure and display the gas concentration at induction and at the point of maximum gas concentration
  • the time of exposure should also be displayed or indicated
  • so animals can be visually monitored during the induction phase for any behaviour indicating distress from adverseness to the inhaled gas (agitation and escaping behaviour)
  • so animals can be accessed if the conveyance system fails, taking into account personnel safety
  • so the adjacent work area is equipped with gas-measuring equipment that continuously measure and display the gas concentrations
  • to provide a visible and audible warning to staff, if the gases used in stunning exceed the maximum allowed in the surrounding work area
  • so the concentration of gases in the work area do not exceed those permitted under provincial and/or federal OSH requirements
  • it is recommended to use the gondola group system for pit type of gas stunning systems since pigs are generally calmer when stunned in groups than when moved in single file to the stunner

Animal welfare PCP for gas stunning for pigs

• The licence holder's PCP should include the following preventive measures, procedures and information:
  • a protocol for animal handling to be carried out by competent employees during pre-stun to minimize stress
  • the gas concentrations and time of exposure are documented in the PCP and selected to minimize the stress of induction of anesthesia
  • gas mixtures and methods that used are those proven to be effective and humane
  • a protocol to monitor the behaviour of animals during the induction of unconsciousness so that corrective actions can be implemented for observable problems:
    • such as animals piling up or falling on top of each, vocalizing or attempting to escape
  • the measures to ensure that exposure time and gas concentration are sufficient to ensure animals do not regain consciousness before death by bleeding
  • corrective action procedures to ensure humane stunning occurs during line stoppages
  • corrective action procedures to ensure that there is well maintained back-up stunning equipment available at all times
  • the procedure including test equipment and frequency for testing the stunning equipment

CAS of poultry

• The licence holder's written animal welfare PCP should include the following preventive measures, procedures and information:
  • monitoring, verification and corrective action procedures to ensure birds are effectively stunned and do not return to sensibility before bleeding
    • in the case of irreversible CAS stunning, the outcome is that the birds are dead upon exit from the container; however this should be verified through validation or documented evidence that this outcome is consistently met
  • every establishment using gas stunning should have a written protocol that is linked to or is part of the establishment food safety PCP to identify DOAs and how identified DOAs are removed:
    • the licence holder may choose to identify and remove DOAs either before or after the CAS step
    • the protocol may be based on an acceptable standard or practice that is derived from documented evidence (such as scientific articles or studies) or it may be the result of validation studies conducted in the establishment
  • the system (including the modules if using a system where birds are not removed) where birds are exposed to the gas and the equipment used to convey them through the system should be designed and maintained to avoid injury and unnecessary stress
  • the gas system should be designed so birds can be visually monitored during the induction phase, throughout the stunning phase and accessed if the conveyance system fails in accordance with the PCP corrective action procedures
  • The following principles apply to humane treatment of the birds for gas stunning:
    • the gas mixtures and methods used are proven to be effective and humane
    • animals should not pile, vocalize, stand or fall on top of each other during the stunning process
    • the behaviour of birds during the induction of insensibility should be monitored, evaluated, and recorded and corrective action procedures taken for deviations
    • there should be an emergency back-up plan in the event of gas stunning equipment or system failure
  • This emergency plan should be well designed to ensure the humane treatment of the birds at all times and the prevention of prolonged periods of time that the birds are without food or water
  • It should include the proper use of well-maintained back-up stunning equipment
  • The operational parameters of the equipment should have a protocol that includes:
    • maintenance of the stunning equipment
    • how the equipment is tested and the frequency of testing
    • methods used to determine the gas concentrations
    • exposure times for the species, the size(s) of birds processed
    • the gas mixtures and methods used are those proven to be effective and humane
  • the establishment should have a protocol in place to identify birds that are conscious upon exit from the gas stunning system, through an effective monitoring procedure, especially if the outcome is not irreversible gas stunning, and ensure the birds are immediately re-stunned or humanely killed

Low atmospheric pressure stunning (LAPS)

• LAPS is a computer controlled patented system that uses slow decompression (vacuum) to remove O₂ (progressive hypobaric hypoxia) to achieve unconsciousness in the birds within the crates that automatically enter chambers; therefore there is minimal handling of the birds and no shackling prior to stunning.
• LAPS may provide the same animal welfare standards not less than the presently accepted methods available.
  • Possible discomfort associated with this method must be controlled through the rate of decompression and O₂
  • Signs of effective stun include ataxia, loss of posture and wing flapping from tonic/clonic convulsions caused by the anoxia.

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

• Decapitation of birds can be used to slaughter birds, as a back-up process for birds that have not been properly rendered insensible by another method of stunning, such as an electric stunner or CAS.
• Decapitation is to be performed by trained personnel or effective automatic decapitation equipment, using well maintained equipment (sharp knives or decapitation equipment) as per the licence holder's animal welfare PCP

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

• The licence holder of the slaughter establishment should include written training protocols in the PCP to ensure that personnel who perform the task of stunning are able to check all animals to rule out the presence of consciousness.
• They should be sufficiently trained and competent to monitor every animal after stunning or for poultry, whether most of the birds appear the same when looking down the line, until the animals are bled out and verified to be dead prior to further dressing steps and procedures.
• These trained employees should be able to monitor:
  • signs of return to sensibility for the food animal species and type of stunning equipment or system used
  • signs of potential return to consciousness/sensibility which are evaluated in the context of the whole picture, as a collective assessment and must include enough signs as indicators to make this assessment correctly.
  • This assessment includes understanding that a given sign may be useful if it is present but not always if it absent, for example:
    • Vocalization and spontaneous blinking, when present are reliable signs for consciousness but when absent are not reliable signs for unconsciousness
  • Some signs are useful indicators of both consciousness and unconsciousness, for example:
    • Rhythmic breathing is a useful sign of unconsciousness when absent after electrical and mechanical stunning methods and a useful sign of consciousness or return to consciousness when present
• assessing consciousness/sensibility in poultry can present with challenges because of the high line speeds used in most federal poultry slaughter establishments
  • for practical purposes, groups of birds are assessed for uniformity of signs of consciousness or unconsciousness to gain an idea of whether stunning is effective
• effectiveness of stunning is evaluated on an outcome basis (no signs of return to sensibility)
  • however the signs of return to consciousness are progressive so it is important not to wait before implementing deviation procedures when observing any of these signs of consciousness during the monitoring procedures on an ongoing basis
  • the signs of consciousness/sensibility or unconsciousness/ insensibility vary with the species and the method of stunning used
• the licence holder should include as part of the animal welfare PCP for poultry, effective measures for ensuring all birds are effectively stunned and no conscious birds enters the scald tank alive as the key outcome to prevent avoidable suffering to the individual bird
  • This includes the monitoring for signs that no birds are returning to sensibility at any point prior to entering the scald tank, including during the bleed-out step
    • monitoring at more than one point on the line is ideal and should include right after the stunning procedure and at some point during the bleed out process prior to the birds entering the scalding tank

Cutting and bleeding methods for conventional slaughter

• the outcome of effective cutting and bleeding of all food animals is to result in death through exsanguination of the animal with all methods of stunning, especially if there is any potential for the stunning to be reversible
• this ensures the animal will not regain consciousness during further dressing procedures

Cutting/bleeding of red meat species including ratites

• The licence holder's written PCP should include the following preventive measures, procedures and information:
  • stunned animals are bled out as soon as possible and remain insensible until death
  • the time between effective stun and effective stick is kept to a minimum
  • animals are bled by incising a carotid artery and jugular vein close to the cranial part of the neck, or close to the place from which they arise (chest sticking):
    • chest sticking is strongly recommended as it results in a massive flow of blood rapidly when done properly
    • the blood flow from sticking is adequate to prevent occlusion during bleed out
    • For ostriches and rheas, to promote better bleeding, it is preferable to sever the major blood vessels (jugular veins and carotids) in the caudal cervical area near the thoracic inlet provided the thoracic cavity is not penetrated.
    • Emus may be bled by cutting the major vessels near the cranial part of the neck similar to turkeys
• staff members are able to observe, inspect, and access the animals for emergency re-stunning if required
• during bleed out, if any animal returns to sensibility, the stun and slaughter of all other animals stop, and the situation is corrected immediately
• no scalding or singeing , skinning or dressing procedure is performed on any animal until bleeding is complete and the animal is dead

Cutting/bleeding of rabbits

• bleeding occurs as soon as possible after stunning, especially if head-only electric stun is used
• in general, best practice is under 15 seconds for head-only electric stunning; however since rabbits can return to sensibility rapidly, within 5 seconds is preferable
• bleeding is to be performed by severing at least one jugular vein and carotid artery or by decapitation
  • when cutting the blood vessels using a transverse incision, it is recommended to severe both carotids and jugular veins for rapid bleed-out
• decapitation is only acceptable after effective stunning
• dressing procedures are not started until the rabbit is dead

Cutting/bleeding of poultry

• both carotid arteries and jugular veins of birds should be severed since this is the fastest method of exsanguination and results in rapid blood loss and death
• automated neck cutting requires:
  • operational procedures that ensure birds do not pile up at the entry to the guide bars
  • monitoring the cut to ensure that it is properly placed (below the mandible)
  • birds should be bled within 15 seconds of electric stunning
  • birds should bleed for at least 90 seconds
  • they are monitored on the bleed rail to ensure that they do not return to consciousness
  • they are dead before they enter the scald tank to avoid extreme suffering due to death from scalding if still possibly sensible
  • efficacy of the stunning and automated neck-cutting equipment should be checked by trained personnel each time the line starts up, at the start of each shift and at the beginning of a new lot of birds to ensure stunning and slaughter are effective and humane
  • efficacy of backup stunning equipment is checked at the same frequency to ensure the deviation procedure for failed stuns is working

Uncut red birds and inadequately bled birds

• there is zero tolerance for birds missing the automatic knife and being missed by the backup cutter after stunning methods that have any potential to be reversible
• these animals have a strong possibility of entering the scald tank alive and fully conscious (uncut red birds)
• an uncut red bird represents a failure of the slaughter process
• the cause of the failure should be immediately investigated by the licence holder
• the licence holder should take immediate effective corrective actions to prevent similar failures
• all incidents and related corrective actions should be documented
• inadequately bled birds differ from uncut red birds
• they have a neck cut, but for a variety of reasons, the bleed out is not effective
• the probability, in general, is that these birds were dead before entering the scald tank
• the presence of these mild to brick-red carcasses at the preselection station may be an indication of improper sticking
• when carcasses have been neck-cut but have not bled out properly, the licence holder should evaluate the stunning and killing procedures, develop and implement a corrective action to prevent recurrence

References

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

• Humane stunning and slaughter of food animals and post-cut management
• Additional PCP Content for food animal welfare
• Humane treatment of food animals at the slaughter establishment

CFIA guidelines of best practices:

• Guidelines for Stunning Techniques of Mammalian Food Animals
• Guidelines for the humane care and handling of food animals at slaughter
• Guidelines for animal welfare Preventive Control Plans and self-audits for the slaughter of food animals
• Guidelines for stunning techniques for avian food animals, including ratites

Controlled atmospheric stunning (CAS) references:

• Temple Grandin: Gas stunning of pigs
• EFSA Journal, 2017:
  • Low atmospheric pressure system for stunning broiler chickens
• Temple Grandin: Gas stunning of poultry
• A new humane method of stunning broilers using low atmospheric pressure, Y. Vizzier-Thaxton et al, 2010, J. Appl. Poult. Res. 10L341-348
• Official Journal of the European Union - PDF (1,421 kb), L122, volume 61, May 17, 2018

Electrical stunning references:

• Shields, Sara J., Raj, A.B.M, Journal of Applied Animal Welfare Science, 13:281 – 299, 2010:
  • A critical review of electrical water-bath stun systems for poultry slaughter and recent developments in alternative technologies
• Girasole, Mariagrazia, et al, Ital J Food Saf. 2015 Jun 30; 4(3): 4576:
  • Optimization of stunning electrical parameters to improve animal welfare in a poultry slaughterhouse

General references for stunning and slaughter of food animals:

• Humane Slaughter Association
• Chapter 7.5, slaughter of animals - Article 7.5.7, Stunning methods, World Organisation for Animal Health (WOAH; founded as Office International des Épizooties (OIE))
• EFSA Journal (2004), 45, 1 -29, (English only):
  • Welfare aspects of the main systems of stunning and killing the main commercial species of animals
• Report on good and adverse practices - Animal welfare concerns in relation to slaughter practices from the viewpoint of veterinary sciences, K Von Holleben, M Von Wenzlawowicz, N Gregory, H Anil, Antonio Velarde, P Rodriguez, Beniamino Cenci Goga, B Catanese, B. Lambooij, February, 2010

Monitoring of stunning references:

• European Food Safety Authority (EFSA) publications for monitoring of stunning during slaughter, 2013:
  • Monitoring slaughter of bovines
  • Monitoring slaughter of pigs
  • Monitoring slaughter of poultry
• Recommended Animal Handling Guidelines & Audit Guide: A Systematic Approach to Animal Welfare, North American Meat Institute, Temple Grandin, with North American Meat Institute Animal Welfare Committee, June 2017

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

• Consciousness, unconsciousness and death in the context of slaughter, Part I, Neurobiological mechanisms underlying stunning and killing, Journal of Meat Science, 118 (2016), 133 – 146, Terlouw, Claudia, Cecile Bourquet, Veronique Deiss
• Consciousness, unconsciousness and death in the context of slaughter, Part II, Evaluation methods, Journal of Meat Science, 118 (2016), 147 – 156, Terlouw, Claudia, Cecile Bourquet, Veronique Deiss
• Verhoeven, Merel, Marien Gerritzen, Antonio Velarde, Ludo Hellebrekers, Bas Kemp, Time to Loss of Consciousness and Its Relation to Behavior in Slaughter Pigs during Stunning with 80 or 95% Carbon Dioxide, 2016
• Assessing unconsciousness in livestock at slaughter - PDF (8,635 kb), Merel Verhoeven - WUR
• Temple Grandin – Updated June 2017 to include information on Zone of Transition between fully conscious and unconscious:
  • How to Determine Insensibility (Unconsciousness) in Cattle, Sheep and Pigs