Retrospectacle: A Neuroscience Blog

While reading the June issue of Nature, I saw an editorial piece called Last Rites which touched on a subject which interests me: humane euthanization of lab animals. Our lab does research on guinea pigs (we must be the last lab to *actually* use guinea pigs), and its of the utmost concern to all of us that they feel no pain when they are sacrificed (or “sacked” as we say). There exists two main ways of euthanization: inhaling carbon dioxide gas or by “cervical dislocation” (euphamism for breaking the animal’s neck). The former require little to no researcher interaction, but may be a slow panic-filled death, while the latter requires hands-on participation in the animal’s demise, but it instant and painless. (More below the fold!)

Despite this, the opinion piece states:

In the United States, the institutional animal use and care committees that oversee animal research are likely to demand a “scientific justification” for breaking rodents’ necks rather than gassing them. This is because most of them adhere to guidelines written by the American Veterinary Medical Association (AVMA), which requires such justification, noting that cervical dislocation may be “aesthetically displeasing to personnel” who have to carry it out. This piece of red tape often makes it simpler for US researchers to stick with carbon dioxide.

I find this “justification” requirement disturbing, in that it will require an extra effort on the part of the researcher to fufill the actual objective of the AVMA (assuming it is to oversee the humane care of animals). The fact that some personnel may be squeamish about performing a cervical dislocation is absolutely no excuse for an animal to have a more difficult death.

The issue of how humane carbon dioxide gas euthanasia is was explored in another Nature News piece called Bioethics: An Easy Way Out.

It says:

‘There is a strong suspicion that CO2 levels that in no way cause them pain do cause them distress,’ says [neurophysiologist Huw] Golledge. Given the choice, rats will rapidly get out of a chamber containing CO2 concentrations of about 15% or more — far below the concentration needed to knock them senseless.


Kathleen Conlee of the Humane Society, an animal-welfare organization based in Washington DC, doesn’t need any more evidence. She thinks killing rodents with CO2 alone is cruel, and prefers an anaesthetic gas — or, in cases where the anaesthetic would interfere with post-mortem measurements, the guillotine. “We say, if there is a small number of animals, and the person is well trained, use decapitation. If you are doing a large number, use halothane or isoflurane, and then blast them with however much CO2 you want.” “I feel strongly about it personally,” Conlee adds. “The number of animals is huge; the evidence is here; the alternatives are here. It is a no-brainer.”


  1. #1 Bob
    July 11, 2006

    Have you broken a guinea pig’s neck?

    And if so, would you give an account of the first time you did so?

  2. #2 Shelley Batts
    July 11, 2006

    I euthanize by cervical dislocation with a small guillotine, not by hand. This has more to do with not being confident that I am strong enough to reliably make a clean break with my hands, every time. The guillotine works great though, its VERY fast, and does the job right 100% of the time. I administer a mixture of ketamine and xylazine (Anased) based on weight, which renders the animal completely asleep. We test its reflexes by pinching its toenail hard, if it jerks, we administer more drugs. When it is fully anesthetized, it gets the chop. Some people in my lab who are strong do do it the more traditional way, but always with the ketamine/Anased administered first.

  3. #3 darkman
    July 11, 2006

    there is always a lot of talk surrounding this issue, a favorite topic for science ethics classes everywhere. everyone has their own feelings about what is appropriate and allowed, but really, the method used to sacrifice an animal for research should be wholly dependant on what research is needed (and not on researchers personal feelings). Carbon dioxide is not fast enough for many types of post-mortem studies, for example, trying to get a rat brain for molecular studies before local RNA degrades. And it’s true when they say that gassed animals probably experience stress and fear before death (they exhibit escape behaviors), though it is a physically painless method, increased CORT levels can alter important physiology. And certain anesthetics, both gas and liquids such as isofluorane or pentobarbital, can also interfere with neural physiology, expecially if studying drug effects. Both the guillotine and cervical dislocation are a little startling for first timers, but squeamish or not, these are accepted and necessary techniques that cannot be disallowed. Most of the time they’re the best method for sacrificing research rodents. I have enough to worry about with PETA raiding my lab than to have to worry about uneasy researchers not wanting to use the lab guillotine. There are other animal models for the squeamish, I’m sure they’d all love to work on the fruit fly or zebrafish.

  4. #4 Shelley Batts
    July 11, 2006

    Yep, somebody once said to me “If you’re allergic to white lab coats you shouldn’t be working in a hospital.”

  5. #5 Brian
    July 11, 2006

    Cervical dislocation is ‘aesthetically displeasing,’ but the real reason not to do it as a matter of course without anesthetics is that it’s very easy to screw up, even if you’re trained. There were a number of occasions when we ran out of CO2 and I had to do dislocations on my mice, and you have to be very careful. Of course, you could always just do isoflurane into CO2, but the respiratory depression would make it take a while – which, when you’re dealing with 10 mice and a 9 hour procedure after they’re sacked, 10 minutes per mouse is a little irritating.

  6. #6 Incitatus
    July 11, 2006

    What Darkman said. My Ph.D supervisor was very clear on the matter of killing animals; it doesn’t matter how much mess you make or how queasy it makes you feel, what matters is that the animal suffers as little as possible, and that you don’t bugger up the tissue you wish to isolate.

    As for the use of CO2, it certainly is distressing. One only has to take a good breath over a bucket of dry ice to experience it. Apparently.

  7. #7 Shelley Batts
    July 11, 2006

    Now now Incitatus, don’t go around sniffing dry ice to make your point. 🙂

  8. #8 Mark
    July 12, 2006

    I work in engineering (my dad did lab animal work in the army, but that’s a whole different story), but it seems nitrogen would be much more humane as I hear it doesn’t cause the suffocation panic like CO2. I’ve heard stories about welders accidentally hooking up pure nitrogen to their respirators instead of air, causing them to simply drop dead without any warning signs at all.

  9. #9 CK Loo
    July 12, 2006

    In the lab I worked in the rats and mice were for the most part put down with an overdose of barbiturate. Though, we had a guillotine as well but I never used it (I never had to use cervical dislocation to put down any of the animals).

  10. #10 Peter
    July 13, 2006

    I’ve done some histology on rats and mice in a neuroscience lab in the UK a few months ago. I think there a huge difference in legislation surrounding animal use in reasearch between the UK and the states. As far as I understand, British law is much more restrictive and clearly demands the use of the most humane way possible to euthanise the animals. Physical methods are preferred, as they are much quicker and cause less discomfort. At least for the animal.

    We did some large scale studies involving many mice and the only methods we routinely use were stun and decap (decapitation by guillotine) or straight decap. For people who perform these methods (and cervical dislocation) routinely, there is very little risk of mistakes. I once used pentobarbital, for the purpose of transcardiac perfusion. It takes time to act and (I obviously cannot be sure of what a mouse feels but…) I imagine gradually losing control and feeling in the mouse’s limb could be very distressing for it.

    By the way, some of the neighbouring labs did use guinea pigs! I even got a quick lesson in handling them. They must be the most phlegmatic animals of all!

  11. #11 Shelley Batts
    July 13, 2006

    Guinea pigs are really docile. Its probably impossible to get bit by one. I just roll them over and give injections, and they hardly even notice. Much more preferable to rats and mice which bite like the dickens.

  12. #12 Peter
    July 13, 2006

    PS Another important practice is to try to keep the surroundings the same during the procedure, to handle the animals in the same way as they are handled day-to-day. A thought that always bothers me – what kind of thoughts are going through the little head of the last mouse that’s left in the cage?

  13. #13 Shelley Batts
    July 13, 2006

    Well, apparenly now they can emphatize, or whatever (see the SEED sidebar for the link). I think thats BS though, but I can’t go against the hand that feeds, now can i? 🙂

  14. #14 CK Loo
    July 13, 2006

    I actually found that rats aren’t apt to bite (well at least not Long-Evans Hooded rats). If you swing them a little they get really docile. Mice on the other hand are little bastards. Especially MAO-B KOs, they’re exceptionally ornery. I used to get bitten bad enough to draw blood every time I took them out of their cages. Though, it could be just that they like the prospect of getting wires poked into their heads. If someone tried to use me for a intracranial stimulation study I’d probably bite them too.

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