Pain and distress during CO2 euthanasia

Joanna Makowska

UBC Animal Welfare ProgramTHE UNIVERSITY OFBRITISHCOLUMBIA

THE UNIVERSITY OFBRITISHCOLUMBIA

ANSC 500

March 3rd 2008

In Canada, over 2.5 million laboratory animals used in 2006

332,000 rats (13%)911,000 mice (36%)

UBC Animal Welfare Program

The most frequent laboratory procedure

Most common for rodents: CO2 2 methods:

Pre-fill Gradual-fill



Definition:

Greek “eu” = good and “thanatos” = death

Killing animals without pain or distress

Welfare implications

Key questions:

3) Does CO2 euthanasia cause PAIN?

4) Does it cause DISTRESS?


Humans: pain at > 40% CO2 Rats: activation of nasal nociceptors at > 40% CO2

CO2 converted to carbonic acid in mucosa

Acid causes burning sensation

CO2 + H2O H+ + HCO3-


Humans: nasal irritants cause bradycardia (slow

heart rate) at >40%

Does it occur during CO2 euthanasia?


Rats exposed to: Pre-fill (100% CO2) Gradual-fill (20% chamber volume/min)

Recorded: EEG (brain activity) ECG (heart activity)


Golledge et al. 2005


BradycardiaUnconsciousness

Death


Potential for 10 sec of pain


BradycardiaUnconsciousness Death


No pain

Key questions:

3) Does CO2 euthanasia cause PAIN?

4) Does it cause DISTRESS?


Behavioural responses to CO2:

Nose to lid contactRearsEscape behavioursVocalizations



Niel & Weary 2006

(Video of a rat’s behaviouralresponse to CO2)


Niel & Weary 2006

Compares motivation for a reward against motivation to avoid gas exposure



(Video of a rat running the task)

Rats exposed to: Pre-fill Gradual-fill

Recorded: Time to leave the test cage CO2 concentration when left the test cage


Niel & Weary 2007

http://images.google.com/imgres?imgurl=http://www-math.cudenver.edu/~wcherowi/clock.gif&imgrefurl=http://www-math.cudenver.edu/~wcherowi/clockar.html&h=319&w=305&sz=4&hl=en&start=1&um=1&tbnid=bD10gaSQkcUu6M:&tbnh=118&tbnw=113&prev=/images%3Fq%3Dclock%26ndsp%3D20%26svnum%3D10%26um%3D1%26hl%3Den%26rls%3Dcom.microsoft:en-ca:IE-SearchBox%26rlz%3D1I7GGLR%26sa%3DN


Niel & Weary 2007


Niel & Weary 2007

17

Carbon dioxide

(%)

Flow rate (%/min)

Behavioural responses Escape behaviours begin at 10% and peak at 20% Loss of consciousness at >30%

Approach-avoidance testing CO2 exposure is aversive to rats, starting at 15%


Dyspnea is a discomfort caused by the urge to breathe In humans, starts at 7% CO2 Severe at 15-20% CO2

Consistent with rats’ aversion thresholds


UBC Animal Welfare Program UBC Animal Welfare Program

High CO2 causes pain

Low CO2 causes distress (dyspnea?)

ALTERNATIVES ARE URGENTLY NEEDED

Any questions?

Education

Pain and distress during CO2 euthanasia