Electrical and CO2

Stunning, Handling, and 

Determining Insensibility 

in Pigs and Sheep, 

2

nd Edition

Temple Grandin

Department of Animal Sciences

Colorado State University
Humane Slaughter Act

All animals are rendered 

insensible to pain by a single 

blow or gunshot or an electrical 

chemical, or other means that 

are rapid and effective
All Methods of Stunning

Definitely Conscious

• Remains standing

• Head or body right reflex

• Voluntary vocalization

• Spontaneous blinking (do not confuse 

with nystagmus)

• Eye pursuit

• Response to threat test-No touching

(Terlouw, et al., 2016)

If any one of these indicators is present, 

the animal is conscious. 
All Methods of Stunning

Definitely unconscious – Brain dead

Absence of corneal reflex to touch

Absence of eyelid reflex to touch

Absence of rhythmic breathing (do not 

confuse with gasping)

(Terlouw et al., 2016; Verhoeven, et al., 2016)
All Methods of Stunning

Situations where a second shot application of 

the electric stunner prevents return to 

sensibility.

Weak corneal reflex

Eyelid reflex

Rhythmic breathing

All indicators of definite consciousness must 

be absent.
All Methods of Stunning

Before invasive dressing procedures start after 

bleeding

All indicators of definite consciousness and 

definitely unconscious or brain dead must be 

absent
Trouble Shooting 

Handling

1. Distractions that cause balking

2. Slick floor causes agitation

3. Facility design problem

4. Employee training issue

5. Lame pigs

6. Pens not walked 

on the farm
Most Common 

Distractions

1. Reflections on water or metal

2. Air blowing towards approaching pigs

3. Moving people or equipment

4. Chute entrance too dark

5. Visual cliff in conveyor restrainer
Electric Prod Use on Pigs Was Reduced By 

Adding Lighting at the Restrainer Entrance

All handlers 

were well 

trained and 

only pigs that 

balked or 

backed up 

were prodded
Indirect Lighting 

Works Best

This lamp is pointed in the same

direction as the pigs
Pig Baulking at 

Metal Strip
Quiet 

handling in 

the stunning 

chute

= 10 %

less PSE
Benjamin et al., 2001

Aggressive Handling

Quiet Handling

25 mmol/L

4 mmol/L

Blood 

Lactate
Humane Slaughter Regulations

9 CFR.313.2

Driving livestock “minimize excitement 

and discomfort”

“Any use of such implements (referring 

to electric prods or other driving 

implements) which, in the opinion of 

the inspector is excessive, is 

prohibited”
Big Question: When Does 

Tapping Become Beating?

Video “Proper Use of Livestock Driving 

Tools with Temple Grandin”

Demonstrates hitting an empty corrugated 

cardboard box. When it starts to crush, 

tapping has become beating.
Training 

Employees

1. Flight Zone Principles

2. Point of Balance

3. No Yelling

4. Move Pigs in Small Groups

5. Fill Crowd Pen Half Full

6. Get Electric Prods Out of People’s 

Hands
Use 

Alternative 

Driving Aids
Trouble Shooting 

Electric Stunning

1. Excessive electric prod use 

due to distractions

2. Stunner settings

3. Employee training

4. Wand ergonomics

5. Line speed

6. Poor bleeding
Both sides of restrainer must 

run at the same speed
Two Types of 

Electric Stunning

Head Only – Must bleed 

within 15 sec.

Cardiac Arrest – Must bleed 

within 60 sec.
Head Only Reversible 

Stun Correct Position
The extended wand tips and extra 

star wheels (spurs) assure correct 

stun wand contact with brain

Locate wand as close to the 

ear as possible, in the thin 

crevice. Note that this wand 

has two sets of star wheels for 

small and large pigs

Longer, wider wand tips help 

to facilitate secure contact on 

the head of larger pigs

Credit: Erika L. Voogd
For pigs larger than 200 pounds, 

extend wand tips to assure 

correct stun wand contact

Extended tips with extra star wheels. Stainless steel 

star wheels (spurs) conduct better than carbon steel

Credit: Erika L. Voogd
Procedure for Small Plants

After head only 

stunning, apply 

electrode to the 

heart to prevent 

return to sensibility

Vogel et al., 2010
Insulate the stun box to prevent 

grounding during stun

Truck rubber mats on 

floor and wall. 

Coated metal gate

Plastic lining in stun 

box area to insulate 

electrical current

Credit – Erika L. Voogd
Head to body cardiac 

arrest stunner
In small plants, many pigs that are head only 

stunned regain sensibility because the hoist is 

very slow. A simple solution to the problem is 

to apply the stunner to the head first and then 

apply it a second time to the chest to stop the 

heart (photograph courtesy of Erika Voogd)
Incorrect Head/Heart Saddle 

Stunner Placement
Electrodes must be positioned so 

the current goes through the brain

Location of 

Pig Brain
EEG brainwaves used to determine 

that a proper stun induces 

a grand mal epileptic seizure
Minimum Stunner 

Amperage Settings 

1.25 amps for pigs

1.00 amps for sheep and cattle


Blood Splash Caused By 

Poor Electric Stunning
Center Track 

Restrainer 

May have less 

blood splash

than a V Conveyor 

because 

there is less

pressure 

on the body
Electric Stunning Troubleshooting

Blood Splash (manual and automatic)

1. Sliding wand during the stun

2. Hot wanding

3. Frayed wires inside the cords

4. Corroded switches

5. Water in switches or cords

6. Dirty electrodes

7. Animal grounds out through restrainer

8. Hold Down pushing down on the animal

9. One side of restrainer runs faster

Blood splash trouble shooting
Automatic Electric 

Stunners
Properly 

Stunned 

Insensible 

Pigs
Righting Reflex in 

a Fully Sensible Pig

Picture not from U.S.
Differences in Reactions 

of Insensible Animals

Nystagmus (vibrating) eye must not be confused with 

natural spontaneous blinking. Nystagmus is permissible 

after electric or CO2 stunning. It must be absent after 

captive bolt.

Gasping like a fish out of water must not be confused with 

true rhythmic breathing. Gasping is permissible after 

electric or CO2 stunning. It must be absent after captive 

bolt.

Corneal Reflex must be completely absent after captive 

bolt.
Interpreting Eye Blinks in 

Electrically Stunned Pigs

Under plant conditions, avoid touching the eye with 

fingers. Watch for normal blinks which look like 

blinks on a live pig. The following are not blinks:

1. Nystagmus – vibrating eye or lid

2. Eye clenched shut – pops open

3. Opens when touched but does not close

In captive bolt stunned cattle, nystagmus 

is a sign of a possible poor stun 
Troubleshooting Return to 

Sensibility Signs in Electrically 

Stunned Animals

1. Insufficient amperage

2. Poor bleeding

3. Poor initial contact that results in insufficient time

4. Interrupted current which results in insufficient time

5. Wrong placement on the head

6. Stunning-to-bleed interval too long with head only 

stunning

Trouble shooting return to sensibility
Improving Stun Wand 

Surface Area Can Increase 

the Stun Efficacy
Prone bleed may reduce blood 

splash because the stun to bleed 

interval is under 10 seconds
Bleeding

Good bleeding with Poor bleeding with

high blood flow small blood flow
Correct position for shooting swine with a 

captive bolt or a firearm. Many old 

diagrams show a position that is too low 

(diagram by J.K. Shearer)
Captive Bolt Stunners for 

Non-Ambulatory Pigs are 

Often Neglected

Store cartridges in a dry place 

and bring to the yards, a oneday supply of cartridges

If the stunner has been used, it 

must be cleaned and serviced at 

the end of the shift
Genetics May Affect 

Pig's Reaction to CO2

CO2 Stunner
Low Stress Group 

Handling With CO2
Best Practice:

Inspection port 

on CO2 machine 

for observing 

anesthesia induction
Control of forward movements 

of crowd gate by a person 

prevents overcrowding
CO2 Pigs Limp and Floppy

Slight limb movements and 

gasping may occur
Order of Events During Return to 

Sensibility in CO2 Stunned Pigs

Average Time

Corneal reflex (touch eye) 42 sec

Rhythmic breathing 68 sec

Excitation 76 sec

Nystagmus (vibrating eye) 86 sec

Spontaneous natural blinking (don’t touch) 93 sec

Conscious movement (righting reflex) 171 sec

Attempt to stand up 387 sec

These events are very variable

Danish Meat Research Institute, Holst (2001)

CO2return to sensibility sequence
There is Zero Tolerance 

for Hoisting an 

Animal that is Showing Obvious 

Signs of Sensibility

There is Zero Tolerance for :

Skinning, Scalding, Dehairing or 

Removal of any Body Part 

on an Animal that Shows any Sign of 

Partial Return to Sensibility

It MUST be brain dead
Signs of Brain Death

No corneal reflex

Do not use finger – must use pen

Eyelash reflex – Touch eyelashes only

No rhythmic breathing

Do not confuse with nystagmus (vibrating 

eye)

Do not confuse with grasping
Numerical Scoring System for Cattle 

Minimum Acceptable Percentages

Stunned with one captive bolt or gun shot 95%

Insensible 100%

Electric prod - Acceptable 25%

Electric Prod – Excellent 5%

Falling down 1%

Vocalizing 3%

Vocalizing with head holder 5%
USDA/FSIS Robust Systematic 

Approach for Humane 

Slaughter Requirements

Written Procedures – SOPs for staying in compliance, 

includes corrective action for a noncompliance

Written Records of evaluations, internal NAMI audits, 

stunner maintenance log and employee training

FSIS – Review of records and written procedure

Is similar to a HACCP Plan
USDA/FSIS Definition of 

Egregious Inhumane 

Treatment

“An egregious inhumane treatment 

is any act or condition that results 

in severe harm to animals.”

FSIS Directive 6900.2, Revision 2
Useful FSIS Sources 

on the Internet

FSIS Compliance Guide for Systematic 

Approach to Humane Handling of 

Livestock, 2013

Humane Interactive Knowledge Exchange 

(HIKE) Scenarios

Humane Handling Enforcement Actions –

List All Regulatory Actions

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