Pain: Abolishing a Necessary Evil

Donald C. Lay Jr. Research Leader

Livestock Behavior Research UnitAgricultural Research Unit, USDA

West Lafayette IN, on Purdue University Campus

Livestock Behavior Research Unit Mission (Agricultural Research Service-USDA)• to develop scientific measures of animal

welfare that will allow an objective evaluation of animal agricultural practices

• to improve existing practices and invent new practices that can enhance animal welfare and increase animal productivity

Publications on “Farm Animal Welfare”(18,521, Science Direct)

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Mounting Regulation, Policy, Standards and Assessments

• Tyson Announcement, Jan. 8th, 2014– Stop the use of Blunt Force Trauma

– Eliminate or reduce pain from tail docking and castration

• Producer Groups and External On-Farm Assessment Programs

Skin

Dorsal gray horn (Spinal cord)

Reticular formation (Brain stem)

Thalamus (Diencephalon)

Somatosensory (Cortex)

A, C -fibers

Injury

Skin

A-, C-fibers

Cheng, 2005; Modified from Neuroscience Exploring the brain, 2001

Pain in Humans

A-thickly myelinated = fastC – unmyelinated = slow, polymodal

Cheng, 2005

Pain Mediators

Function of Pain• Adaptive evolutionary strategy to protect the

body.– Early warning system.

– Allows animals to learn what not to do.

– The more intense the pain, the greater the threat.

• Non-adaptive pain.– Pain that persists after trauma is healed.

– Neuromas and other neuropathic pain

CIPA and HSANCongenital insensitivity to pain with anhidrosisHereditary Sensory and autonomic neuropathy

• Never feel the stick of a needle

• Never feel a cut or a burn

• Never feel hunger

• Never feel uncomfortable in a chair

Pain is Necessary!

• Babies gnaw their fingers bloody• Poke their eye so hard as to cause abrasions• Lean on hot surfaces to cause 3rd degree burns• Most die before 3 years of age• Cause of death

– Heat stroke– Dehydration– Fever– Blood poisoning

Pain is difficult to measure• Pain has both physiological and psychological components.

• Animals cannot communicate verbally regarding their sensory and emotional experience.

• Pain can be overridden with other feelings, such as fear, fighting, and feeding motivation ….

• Pain is also affected by multiple factors, such as genetic strain, age, production status; environments, and lesion and lesion size.

Neuroanatomy associated with pain in chickens

Sensory receptors

Lunam, 2005

In humans:

• Mechanical nociceptors

• Thermal nociceptors

• Chemical nociceptors

In chickens:

• Herbst corpuscles and • Grandry’s corpuscles• Free Nerve endings

• Behavioral and physiological studies

There are similar behavioral and physiological changes in response to injury between chickens and mammals (Cheng, 2005; Kuenzel, 2007).

• Pharmacological studies

Pain killers (analgesics) can reducepain in both chickens and humans. (Gentle, 1991; Glatz et al., 1992; Paul-Murphy & Ludders, 2001).

Conclusions

• Chickens can feel pain.• Chickens feel pain in a similar

manner to that in mammals.

Definition of pain in animals

In animals• Pain is an aversive sensory and emotional

experience by the animal in response to damage or a threat to the integrity of its tissues (Molony & Kent, 1997; Robertson, 2002; Vinuela-Fernandz et

al., 2007)

In humans• Pain is an unpleasant sensory and emotional

experience associated with actual or potential tissue damage (Merskey and Bogduk, 1994)

Pain can be recognized and assessed indirectly• Physical parameters

Body score (body injury) Growth rate

• Physiological parametersNeurotransmittersNeuropeptides

• Behavioral parametersGeneral behavior (eating, drinking)Guarding behavior (protect injured areas)

Neuroma Trigeminal ganglia Beak

Normal nerve fibers

Regrowth

Neuroma

Degenerating of neuroma

Neuromas may increase pain sensitivity --- chronic pain

Soma Fibers Terminals

Ending of beak stump (post-trimming)

Tissue Scar

Targets

Target

NeuromasHistological characteristics

A neuroma is a tangled mass of a damaged (cut) axon terminal inside the injured area.

Consists of unmyelinated fibers, and then becomes myelinated fibers (A-fibers)

Physiological characteristics

A source of substantial ectopic firing (spontaneous pain)

Increase pain sensitivity

Painful Situations in Agriculture

• Controllable– Beak Trimming– Castration– Tail docking– Branding

• Uncontrollable– Birth– Accidents– Injury

Analgesics are Beneficial

Coetzee et al., 2012

Bulls castrated without analgesic (meloxicam) show a greater incidence of Bovine Respiratory Disease

Why not just use analgesics?

They would need to be:1) readily available and registered for use2) easy to administer3) quick and long acting4) have short withdrawal periods5) show return on investmentOnly 1 approved anti-inflammatory in the U.S. for swine and cattle; a few for cattle and swine in E.U. and U.K.

Schwartzkopf-Genswein et al., 2012

Cannibalism will Increase in Prevalence with More Space

a

c

N. intramand.

N. ophthal. med.

C

Predicted Levels of Behavioral Expression+none or incomplete, ++low, +++moderate, and ++++full or high

1 Furnished Cage Non-cage (Barn) Outdoor

(Free-Range)

Behavioral Opportunities

Conventional Cage

Small

Large

Slats / Litter

Aviaries

Nesting + +++ +++ ++++ ++++ ++++ Brooding + + + + + + Perching + ++ ++ +++ +++ +++ Mating + + + + + + Stereotyped and sham behaviors

++++ ++ ++ + + +

Cannibalism and feather pecking

++ ++ +++ ++++ ++++ ++++

Social aggession

++ +++ ++++ ++ ++ ++

Smothering ++ ++ +++ ++++ ++++ +++ 2

Lay et al., 2010

Infrared trimmed

ControlHeated blade trimmed

Does Beak Trimming Cause Pain? Funded by AFRI

Control

Hot Blade trimmed

Infrared trimmed

Drinking Behavior During Warm Water Pain Test

Infrared Beak trimming has been adopted by the United Egg Producers, 2010

Five Weeks Later!

Hen Behavior is Positive but ……Keel Bone Fractures

• 46 % to 90 % have fractures

Nicol et al, 2010

Effect of Analgesic on Perching Behavior of Hens with Keel Bone Fractures

Late

ncy

to la

nd

First two bars are hens with and without analgesic that do not have fractures.The second two bars are hens with and without analgesic that do have fractures.

Nasr et al, 2012

Routine Piglet Processing

• Soon after birth, piglets undergo processing procedures, which are likely sources of stress:

- Teeth resection- Tail docking- Identification- Iron administration- Castration

• For each process, there is a choice of methods

Marchant-Forde et al., 2009 Funded by the National Pork Board

Objectives

• To evaluate stress responses evoked by two alternative methods performed singly: – Teeth (TR) – clip vs. grind – Tails (TD) – cold clip vs. hot clip – Identification (ID) – ear notch vs. ear tag – Iron (FE) – injection vs. oral paste – Castration (CA) – cords cut vs. cords torn

Results

• To evaluate stress responses evoked by two alternative methods performed singly: – Teeth (TR) – clip vs. grind – Tails (TD) – cold clip vs. hot clip – Identification (ID) – ear notch vs. ear tag – Iron (FE) – injection vs. oral paste – Castration (CA) – cords cut vs. cords torn

= worse

Conclusions

• Carried out singly, we can identify which method has least impact on piglet welfare

• Carried out together, it’s much less clear

• The key combination is accuracy and speed

Piglet Aversion to Euthanasia Gases

1

3 3

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7

90% Carbon Dioxideor70:30 mixtures of:

Nitrogen:Carbon DioxideNitrous Oxide:Carbon DioxideNitrous Oxide:Oxygen

Rault et al., 2012, in pressFunded by the National Pork Board

Euthanasia: Stress and DeathTwo-Step Procedure

Gas treatment CO2 N2/CO2N2O/CO2 N2O/O2

p-value

Transfer from

treatment to CO2

chamber (seconds) 2.9 ± 0.3a 6.4 ± 0.6b 6.7 ± 1.0b 14.7 ± 2.1c

0.001

Time to death after transfer (seconds) 7.8 ± 1.3 7.6 ± 1.0 5.6 ± 0.3 9.3 ± 1.2 0.20

Total procedure duration (seconds) 10.8 ± 1.3a 13.9 ± 1.2a

11.3 ± 1.4a

24.0 ± 3.0b 0.005

Rault et al., 2012

EEG and Euthanasia

Carbon Dioxide

Nitrous Oxide

Lameness in SowsExercised sows will have:

– An increase in bone density and an increase in muscular weight compared to control sows

– An increase in osteoblastic activity and a decrease in osteoclastic activity compared to control sows

– Improved condition of joints and hooves compared to control sows

Lameness in Sows will Likely Increase with Increase Movement

Loose housing of Sows will likely acerbate this problem as the increase in movement will provide opportunity for torn cartilage to worsen.

Tail Docking Practice in Dairy Cows

Introduced in 1990s in New Zealand to combat Leptospirosis

DOCKED INTACT

Behaviors Recorded:

Tail Swing, Weight Shift, Foot Stomp, Tail CurveEicher et al., 2000

Are Docked Tails more Sensitive to Heat and Cold?

Bottom Line:

Docking causes pain, but less pain in adult cows.

Docked cows have more flies and avoidance behaviors.

Docked tails show signs of neuromas (possibly painful).

Docking doesn’t decrease somatic cell counts.

Conclusions

• Life without pain doesn’t exist.• We recognize that animals feel pain.• Our responsibility is to alleviate or minimize

pain.

• We support future efforts to develop management tools to minimize pain and create alternative practices that alleviate pain.

Thank You

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