Small-Scale Poultry Stunning
Anne Fanatico, Ph.D.
National Center for Appropriate Technology
February 2009
Poultry are not included in Humane Slaughter Act
However,
Birds should be stunned before slaughter because they feel pain
Electric stun is not a painful shock”, insensibility is instantaneous
Birds should be insensible to pain at the time of slaughter
Neck cut without stun, bird stays conscious for at least 15-30 seconds
This suffering is avoidable.
Restrain
Stun/Kill
Bleed
Restraint/Immobilization
Position the bird for kill/stun
Protect carcass quality by reducing wing flapping and convulsions
Methods
•Manual
•Shackles
•Kill cone
Gas stun/kill generally uses a container
Humane slaughter
Slaughter that occurs without causing avoidable fear, anxiety, pain, suffering, distress
(Raj seminar)
Stun
Not required by law for poultry
•Large plants: Universal (to immobilize bird and reduce carcass damage)
•Small plants: Common
•Small farms: Rare
Welfare programs require stunning
Birds feel pain and should be insensible at slaughter
Stun method should induce immediate loss of consciousness (Raj seminar)
Stun should be longer than time interval between stun and neck cut (at least 40s)
Zero tolerance for birds entering scalder alive
Religious kill does not stun: kosher or halal
Stunning and Immobilization
Electric stunning immobilizes bird
and positions it for automatic
killer
Stunning also reduces
massive involuntary
wing flapping and muscular
activity that may damage
carcass and meat quality
Types of Stun/kill
• Electric
Waterbath, group
Whole body
Handheld, individual
Stun knife, whole body
Electrodes, head-only
• Mechanical
•Penetrative captive bolt
•Nonpenetrative captive bolt (concussive)
•Firearm with free projectile
•Maceration (only for embryos and young chicks)
•Cervical dislocation
• Gas
• Atmosphere
Electrical
Electrical stun must be instantaneous
Head only
Causes a generalized epilepsy
Severe wing flapping if unrestrained (Gregory, 2004)
Whole body
Exposes the body to a current generating a generalized epileptic form
and, possibly, fibrillation or stopping of the heart (killing)
Currents travel through paths of least resistance (skin, breast muscle, cardiac
muscle, leg muscle
(abdominal fat has greatest resistivity of tissues)
As a result, muscle contractions (tonic spasms and tremors) are stimulated
Heart and respiratory rates decrease and blood pressure increase (Bilgili 1992)
Majority of current may pass through body (only 20% through head) (Raj seminar)
Impact on meat quality
Signs of effective stun
•Absence of rhythmic breathing
•Absence of third eyelid reflex
•Constant rapid body tremors
•Wings held tight against body
Signs of ineffective stun/kill
•Rhythmic breathing
•Tension in neck
•Ability to control head
•Third eyelid reflex
Signs of effective kill
•Absence of rhythmic breathing
•Absence of third eyelid reflex
•Wings droop
•Dilated pupils
Recoverable stun commonly used in US
Regular breathing returns (signaled by return of
abdominal movements in vent area)
Bird should be cut and bled before recovery
Low voltage electric stun results in:
Epileptic seizure phase
All or nothing threshold event;
Can occur as low as 8 mA (notes)
Although 45 mA needed for effective immobilization (Bilgili 1992)
Theorized that epileptic waveform are insensible to pain and are unconsciousness
Humans who have experience of grand mal or epileptic seizure report no pain
Electrical circuit should be in form of a closed loop
Electrical stun parameters
Impact of waveform (AC, DC constant, DC pulsed)
Impact of frequency (Hz, waveform per second) (household currents at 60 Hz)
Impact of amount of current or amps (mA) or voltage (V)
Period of time stun is applied
Amps do the actual stunning
Electric Water bath Stun
Causes epileptic waveform
In Europe, causes cardiac arrest
Electrical circuit passes
through whole body
Electric Water bath Stun
U.S.
Low voltage stun used
30-60 V, 20-45 mA/bird
Recoverable stun
Europe
High voltage stun used; stun to kill (for welfare reasons)
150 V, 100 mA/bird (Bigili, 1999)
Causes 90% heart fibrillation
Over 120 mA can cause carcass damage (Wilkins, 1999)
However carcass and meat quality issues can result from high voltage stun
Increased breast muscle hemorrhages
Red wingtips
Broken pectoral bones (clavicle, scapula)
Use of high frequency can reduce problems (increase from 60 Hz to 500 Hz)
However, birds only stunned rather than killed by cardiac arrest
Use constant current rather than constant voltage (Raj seminar)
Electrical Water Bath Stun Welfare Issues
Handling can be problematic: Dumping, inversion and shackling live birds
Pre-stun shocks possible
Inadequate stun possible
Mis-stun (flock uniformity issues, insufficient feet-shackle contact (heavy scales
on feet, not wetting feet-shackle contact point, wet birds (causes current to
flow over surface of bird);
high variation in resistivity of skull depending on thickness and density)
Live birds may enter scalder; no red birds (associated with short bleed out time)
Stunning monitors (anmeter) can help insure adequate stun (Gregory, 2004)
Bleed for 90 s (Bilgili 1992)
Handheld Electrical Stunning
Stun knife
Electrical circuit passes through whole body
Uses a metal grounded support (i.e. hang bird from a shackle
Current runs through entire bird (whole body stun)
Usually delivers about 200 mA, depends on setting
Problem:
There are no protocols for
use with animal welfare in mind
Little metering is done
To determine volts and amps
Handheld electric stunner:
Head Only
Two electrode pads on forked handset
Head-only stun
Delivers 130 volts
Available in Europe
Problem: when converting to US
Electricity, amps and volts may change
Captive bolt
Stun/kill
Cartridge-powered
One person can restrain and stun birds
Two people required for adult turkeys
Generally used for euthansia
Air-powered
.22
Penetrating captive bolt
Severe wing flapping; may
be reduced in a cone
maximum pressure of 135psi
http://www.acclesandshelvoke.co.uk/cashpoultry.htm
Amount of air pressure needed for various bird types
Knocker
head type
Flat
Convex
Broiler
Hen
Air pressure
(PSI)
110
110
Broiler
Hen
Turkey (adult)
Turkey (poult)
http://www.acclesandshelvoke.co.uk/cashpoultry.htm
120
120
135
60
Knocker head
Convex or
Flat
http://www.acclesandshelvoke.co.uk/cashpoultry.htm
Position instrument at right angle to skull
Hold beak loosely; release grip when firing
http://www.acclesandshelvoke.co.uk/cashpoultry.htm
Flat or convex knocker head
http://www.acclesandshelvoke.co.uk/cashpoultry.htm
Cartridge components must be cleaned after use
http://www.acclesandshelvoke.co.uk/cashpoultry.htm
http://www.acclesandshelvoke.co.uk/cashpoultry.htm
Captive Bolt: Concussive
Zephyr Stun Gun for Rabbits
Modified nail gun
Compressed air-driven,
non-penetrating captive
bolt to humanely stun rabbits
Place stun gun between
ears at top of skull
Use minimum of 55 PSI
Large rabbits:
Increase PSI
Two shots in quick succession
Zephyr is 99.6% effective when
used correctly
Nonpenetrating captive bolt; concussive
Bleed animal quickly before consciousness returns
Not recommended for euthanasia because animal may return to consciousness
Modified nail gun vs captive bolt gun
Nail gun pushes; must hold head
Leaves wound size of quarter; little bleeding
Gas stunning
Large scale
Advantages:
Less handling
Birds can be killed in coop
No inversion or shackling
of live birds
Gas-stun
Small scale
Containerized
http://www.fpmne.com/
Gas cart
Gas approaches
Use argon/nitrogen with no more than 2% oxygen
Use argon/nitrogen mixture with no more than 30% CO2 and no more than
2% oxygen
High levels of CO2 (above 30%) is aversive to birds; causes breathlessness;
acid is produced
Anoxia (lack of oxygen)
Leads to carcass convulsions after bird is unconscious (carcass damage)
The use of CO2 at low levels can help reduce motor activity
Two phase approach
Uses CO2 at 30% for anesthesia and then increases to 80% for euthanasia
What if you don’t have any stunning equipment?
•Cervical dislocation
•Rapid decapitation
(Not universally accepted as humane)
(Practice with anesthetized birds; discard meat)
Spinal cord is severed
Carcass issues
Wing flapping, violent muscular contractions
Broken wings, poor bleeding, red discoloration (McNeal, 2003)
Meat quality issues
Convulsions involving wing flapping associated with acceleration in breast
muscle ATP and glycogen depletion and poor water-holding capacity
Watch cervical dislocation demonstration on Humane Slaughter Association video
Impact of stunning on body movement (McNeal 2003)
Variable
Neck cut
Decapitation
Stun,
neck cut
Early (0-10 s)
1.8b
3.3a
1.2c
Intermediate (1060 s)
3.0b
3.9a
2.0c
Late (> 60 s)
2.6a
2.4a
1.9b
Reaction scores
1 = none to mild muscle quivering
2 = mild wing flapping
3 = moderate spasmodic body movement and full wing flapping
4 = violent wing flapping and full-body movement capable of damaging carcass
Results: Body movements that can lead to carcass damage are more violent with
decapitation than neck cut; stunning reduces wing flapping and muscle contractions
compared to decapitation and neck cut
Not stunning
Neck cut: Bird usually loses consciousness within 15 s, but some birds conscious
for 30 s (Gregory, 2004)
Decapitation: loss of brain activity within 15 s (McNeal, 2003)
Factors to consider in stunning/not stunning
•Operator welfare
•Bird welfare
•Bleed out/carcass damage
•Meat quality
Bleeding Efficiency
At neck cut, blood shunted to organs in attempt to maintain homeostasis; only about
half of the volume is lost
Bleeding efficiency depends on
•Blood vessels that are severed
Ventral cut: cuts 4 blood vessels (2 carotid; 2 jugular)
Bilateral cut: only cuts 2 vessels (slower bleeding)
•Size of cut
•Orientation of carcass (vertical position)
•Stun
Low voltage: muscle contractions force blood away from skeletal muscle
towards large vessels for more efficient bleeding
Cardiac arrest can slow bleed out but doesn’t necessarily reduce blood
loss (Gregory)
Bleeding Efficiency
Variable
Neck cut
Bleed out
(Newell and
Shaffer 1950)
45% of
39% of total
total blood blood volume
volume
Source Newell and Shaffer (1950)
Decap
Stun,
neck
cut
Meat Quality Basics
Conversion of muscle to meat
Based on biochemistry
Muscle evolved for locomotion
Muscle contracts, myofibrils interlock (sliding filament); cross bridges form
Muscle does not die immediate at death of animal
ATP is required to break crossbridges of myofibrils
Rigor mortis occurs because myofibril crossbridges cannot be broken after
ATP used up; (until proteins start to degrade)
Meat quality factors
•pH
•Water-holding capacity
•Texture, tenderness
•Color
•Nutrients
•Shelf life
Impact of Stress on Meat Quality
Dark, firm, dry meat (DFD)
Stress sensitive birds may exhaust glycogen stores and, after death, experience
little pH reduction due to low production of lactic acid. This can lead to
dark, firm, dry meat that has a high ultimate pH and is susceptible to bacterial
growth and has a short shelf life.
or
Pale, soft, exudative meat (PSE)
Accelerated metabolism which, when occurring in a carcass that is still warm,
can lead to denaturation of protein and PSE-type meat with poor water holding
capacity and a low ultimate pH.
Rate and extent of pH decline
Rate: You don’t want pH to go down too fast while muscle is hot or denaturation
occurs (PSE)
Degree: You don’t want the pH to be too low (it might get to the isoelectric point)
You don’t want the pH too high (poor shelf life)
Electric stunning slows rigor