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Last updated January 1, 2014

Carbon Dioxide (CO2) for Euthanizing Mammalian Prey

©1995 Dave Parizek


A Note from Melissa Kaplan:
This is an often debated subject in the rec.pets.herp newsgroup and other forums, online and off. One such discussion on RPH prompted large-scale rodent breeder David Parizek to research the matter further. What follows is a copy of his post back to the newsgroup.

It must be noted that use of CO2 gas is not suitable for euthanizing reptiles.

According to the American Veterinary Medical Association's Panel on Euthanasia (Journal of the AVMA, Vol. 202, No. 2, Jan. 15, 1993), the best (=most humane) way to kill rats (and mice) that will be fed to other animals is to asphyxiate (spelling?) them with carbon dioxide gas. Other gases (anesthetics) can be good, but then there could be "accumulation of tissue residues in food producing animals." (= not good to feed to your herps). The report conditionally finds cervical dislocation to be an acceptable method also, as long as the rats are small (less than 200 grams). Bonking, stunning, etc. are specifically listed as NOT considered acceptable. They noted that "data suggest that electrical activity in the brain persists for 13 seconds following cervical dislocation." For this reason, they consider the jury to still be out on the technique. My interpretation is that this is the best technique if you don't have access to gaseous CO2 -- like for the person who needs to kill only a few. However, dry ice can be purchased for around $1.25 per pound at many ice cream shops/ice retailers. If you use dry ice then make sure you don't touch it -- insulate your hands with a towel or something. Similarly, you don't want the rodents to touch it. You should pre-charge the container with the vaporizing dry ice prior to introducing the animals to be euthanized, to make it maximum quick, and to use enough gas -- as only high concentrations have the more humane effects. If you have access to bottled CO2, this is even better.

I have used cervical dislocation in the past on thousands of rodents. Now, since I was prompted to think about the the issue further by my customers (and this thread), I asked around and located the AVMA report, and I now use gaseous CO2 to euthanize mice (I got a used 50 pound bottle and hose for $95 -- they are readily available from fire extinguisher service companies). To me, I was skeptical, but after actually trying it, it does appear to be more humane. The key is to pre-prime the container with the gas, to not agitate them ahead of time (AVMA recommends a quiet setting -- part of what is implied in humane is to avoid stressing the animals). I was surprised and impressed to be honest. I guess, IMHO, that part of the problem with the other techniques is that it is often imprecise. Cervical dislocation usually works well, but the technique actually takes some practice and it doesn't always go perfectly. The CO2 method is humane -- the CO2 method has a "rapid depressant and anesthetic effect" when inhaled in high concentrations. It is not instantaneous, but it is surprisingly fast, and the rodents don't appear to be in pain.

Dave Parizek
Southwest Rodents

Related Articles:

Euthanasia of Reptiles

Notes on Decapitation of of Reptiles

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