Humane Euthanasia of Feeder Rodents
How to humanely euthanize / kill / pre-kill rats, mice, and African soft furred rats
It should be noted that the keeping of carnivorous reptiles almost always includes the feeding of whole prey animals. It is often necessary for the keeper to have appropriate means to euthanize prey animals for safety, quality of life and humane reasons.
It is hotly debated in the reptile and pet community if live feeding is appropriate or inhumane. Some European countries have outlawed live feeding; except when the animal refuses to eat to the point where its life is threatened. Others view the process as nature taking its course, with the carnivore being properly suited through natural abilities to dispatch of the prey animal quickly, and is acceptable in a controlled environment.
While I will avoid the extensive arguments of live vs pre-killed feeding, I will outline some of the socially and humanely acceptable methods for a person to dispatch rodent prey animals that will be fed to reptiles. Either set by the American Veterinary Medical Association or other groups that have studied and reviewed such methods.
Do not perform any of the following methods until you have spoken with a licensed veterinary medical professional.
The AVMA has outlined the considerations taken while evaluating a method of euthanasia.
(AVMA Guidelines on Euthanasia, 2007) In evaluating methods of euthanasia, the panel used the following criteria: (1) ability to induce loss of consciousness and death without causing pain, distress, anxiety, or apprehension; (2) time required to induce loss of consciousness; (3) reliability; (4) safety of personnel; (5) irreversibility; (6) compatibility with requirement and purpose; (7) emotional effect on observers or operators; (8) compatibility with subsequent evaluation, examination, or use of tissue; (9) drug availability and human abuse potential; (10) compatibility with species, age, and health status; (11) ability to maintain equipment in proper working order; and (12) safety for predators/scavengers should the carcass be consumed.” (p. 6)
The number one consideration for a method to be considered humane is that it is conducive to quick loss of consciousness with minimal distress, anxiety, apprehension and pain for the animal.
Carbon Dioxide – CO2 Canister
Cost: Low | Difficulty: Low | Safety: Low risk
The most common and often easiest method is to use carbon dioxide (CO2). The animal is placed in a secure and appropriate container, where the gas is administered in controlled levels until the animal loses consciousness, where death quickly follows. The gas should continue to run for at least a full minute after apparent clinical death to ensure no recovery. In these cases, err on the safe side and let the gas run for a few more minutes in you are unsure of death of the animal.
CO2 is a useful gas to use because of the well documented anesthetic effects. At high concentrations (70-100% concentration) CO2 will increase the pain threshold, and will have a anesthetic effect in 12-50 seconds for rats, depending on concentration used. (AVMA , p. 11)
Euthanasia CO2 Chamber
The chamber should be secure, allow clear visibility of the animals, allow for no overcrowding ( all animals can comfortable lay down, turn and move). The lid should be outfitted with a connection to a CO2 remote line from the canister. One (or two) 1/8″ hole should be in the lid of the chamber to allow excess gas to escape to prevent explosions. The lid should have a foam seal around the lip, and possibly a 1/2″ overhang to ensure a tight sealed fit, so gas only exits the holes in the lid.
The following is an excerpt from the AVMA journal, and I have broken it down into steps to ensure proper euthanasia procedures are followed.
- Species should be separated and chambers should not be overcrowded. With an animal in the chamber, an optimal flow rate should displace at least 20% of the chamber volume per minute.
- Loss of consciousness may be induced more rapidly by exposing animals to a CO2 concentration of 70% or more by pre-filling the chamber for species in which this has not been shown to cause distress.
- Gas flow should be maintained for at least 1 minute after apparent clinical death. It is important to verify that an animal is dead before removing it from the chamber. If an animal is not dead, CO2 narcosis must be followed with another method of euthanasia.
- Additional O2 will, however, prolong time to death and may complicate determination of consciousness. There appears to be no advantage to combining O2 with carbon dioxide for euthanasia. (AVMA, p. 11)
Prefilling a container with CO2 may be more effective for quick loss of consciousness, but it must also be noted that too much CO2 in a short amount of time will build to levels that will react with the mucous linings of the animal and create carbonic acid. This is considered unpleasant for many animals and must be taken into consideration. However, a slow rate of gas released will prolong time to unconsciousness. (AVMA, p. 11)
This method is considerably stress free, moderately quick, and when done properly is irreversable.
Neonatal Animals – CO2 Canister
Cost: Low | Difficulty: Moderate | Safety: Low risk
Neonatal animals are resistant to hypoxia. The CO2 will take longer to euthanize these animals. It is also possible that the prolonged time will allow the CO2 to react with the mucous linings, creating carbonic acid in the animal and may be unpleasant.
Because respiration begins during embryonic development, the unhatched chicken’s environment may normally have a CO2 concentration as high as 14%. Thus, CO2 concentrations for euthanasia of newly hatched chickens and neonates of other species should be especially high. A CO2 concentration of 60% to 70% with a 5-minute exposure time appears to be optimal. (AVMA, p. 11)
For the above reasons, some people will rapid freeze neonatal animals, although the AVMA does not consider it to be humane. “Rapid freezing as a sole means of euthanasia is not considered to be humane. If used, animals should be anesthetized prior to freezing.” (AVMA, p. 39)
We suggest a smaller environment such as a sealable and appropriate container that will allow for small yet high concentrations of 100% CO2 to be administered to maintain 100% CO2 for a period of time, and where the animals can be easily viewed to confirm clinical death. After the suspected clinical death, it may be necessary to prolong exposure to the CO2 environment for up to a half an hour after all movement has stopped. (IACUC, p. 256)
Place the neonatal animals in a plastic bag and without squeezing them, squeeze all of the air out of the bag. Refill the bag slowly with CO2, doing it slowly ensures you do not freeze the animals. Repeat this step two more times to ensure the environment is 100% CO2. Once the bag is full of CO2, seal it and wait until the pups have been motionless and lose color for at least a half an hour. (Sundberg, J. & Boggess, D, p. 68-69) It may be necessary to clip the spine with sharp scissors immediately after removing the animals from the bag to ensure death.
Advantages and Disadvantages
Advantages—(1) The rapid depressant, analgesic, and anesthetic effects of CO2 are well established. (2) Carbon dioxide is readily available and can be purchased in compressed gas cylinders. (3) Carbon dioxide is inexpensive, nonflammable, nonexplosive, and poses minimal hazard to personnel when used with properly designed equipment. (4) Carbon dioxide does not result in accumulation of tissue residues in food-producing animals. …
Disadvantages—(1) Because CO2 is heavier than air, incomplete filling of a chamber may permit animals to climb or raise their heads above the higher concentrations and avoid exposure. (2) Some species, such as fish and burrowing and diving mammals, may have extraordinary tolerance for CO2. …(5) Induction of loss of consciousness at lower concentrations (< 80%) may produce pulmonary and upper respiratory tract lesions.67,84 (6) High concentrations of CO2 may be distressful to some animals. (AVMA, p. 11)
*”Nitrogen and Argon can be distressful to some species (eg, rats). Although N2 and Ar are effective, other methods of euthanasia are preferable.” (AVMA, p. 12) Please do not attempt to use these gases for euthanasia.
The following is not condoned or explicitly discussed by the AVMA, but there are many sources that do discuss the methods about to be described and find them appropriate for humane euthanasia.
The following described methods have been in use by labs and rodent breeding professionals for many years. The use of dry ice may no longer be recommended because of the rising availability of compressed gas, but it is still considered an acceptable alternative when used properly. (IACUC Handbook, p. 254-256)
The following still involve CO2 gassing, and are often the only means by which people are able to humanely euthanize rodents when the recommended equipment is not available to them. I am publishing these methods because I do believe the alternatives are considerably more unethical in domestic situations, have a higher margin of error, and when done incorrectly are extraordinarily inhumane.
Dry Ice Sublimation
Cost: Moderate – High | Difficulty: Moderate | Safety: Moderate risk
The main considerations taken when evaluating the use of dry ice as a means to euthanize are as follows:
- The animal cannot come into direct contact with the ‘dry ice’ nor the container holding the dry ice that can become super cold. (i.e. plastic or metal that can instantly freeze when touched)
- The container for the animals is secure, allows for gas to escape, and offers clear visibility of the animals in the chamber to view clinical death.
- The dry ice is suspended from the ceiling to avoid pooling of the CO2 at the bottom of the chamber prolonging consciousness.
Following is a link to instructions on the use of dry ice sublimation for euthanasia. The first one [was] a video (user has closed account), but I must caution that you should not touch dry ice with bare hands like was done in the video. Please take necessary precautions and wear gloves and safety glasses.
This is a link to a thread that was well written with pictures showing one way to use dry ice as a means to humanely euthanize.
Vinegar and Baking Soda CO2
Cost: Low – Moderate | Difficulty: Moderate | Safety: Low risk
I am currently researching this method and the easiest fool proof way to accomplish; I will post here when I have finished. 3/17/09
Note, it will be much like the set up in the method above, but it is a mess to make CO2 this way and can be time consuming.
Artwohl JE et al. Environmental Conditions in a Chamber with Dry Ice. Contemp Top Lab Anim Sci. 1999 Jan;38(1):67-69. [PMID: 12086455]
AVMA Guidelines on Euthanasia (2007) Retrieved March 17, 2009, from American Veterinary Medical Association Website: http://www.avma.org/issues/animal_welfare/euthanasia.pdf
Biologic Resources Laboratory – Animal Users Manual. Chapter 8, Euthanasia. Retrieved April 19th, 2009, from the brl.uic.edu Website: http://www.brl.uic.edu/ANIMAL_USERS_MANUAL/chapter8/ch8.htm
Committee on Pain and Distress in Laboratory Animals, Institute of Laboratory Animal Resources, Commission on Life Sciences, National Research Council. Recognition and Alleviation of Pain and Distress in Laboratory Animals. (1992). (p. 104 – 108). http://books.nap.edu/openbook.php?record_id=1542&page=104
Conlee KM, Stephens ML, Rowan AN, King LA (2005) Carbon dioxide for euthanasia: concerns regarding pain and distress, with special reference to mice and rats. Laboratory Animals. http://la.rsmjournals.com/cgi/reprint/39/2/137.pdf
Danneman, P. Euthanasia. (2000). In Suckow, M., Silverman, J., & Sreekant M. (Eds.) The IACUC Handbook (pp. 254-256). CRC Press. ISBN 0-8493-1685-5.
Derelanko, M. & Hollinger, M. CRC Handbook of Toxicology. CRC Press; 1995. (p. 25) ISBN: 0-849-3866-83
Donovan, J. & Brown, P. Euthanasia. Current Protocols in Immunology (1995) 1.8.1-1.8.4.
Feldman, D. & Seely, J. Necropsy Guide: Rodents and the Rabbit. CRC Press; 1988. (p. 2) ISBN 0-849-3493-46
Feeder Euthanasia the Easy Way, and Humane too… (2006) Retrieved March 19th, 2009, from Ball-Pythons.net Website: http://www.ball-pythons.net/forums/showthread.php?t=33850
Hackbarth, H., Kuppers, N., Bohnet, W. Euthanasia of rats with carbon dioxide-animal welfare aspects Lab Anim. (2000) 34: 91-96 Institut für Tierhygiene und Tierschutz. PMID: 10759372 Website: http://la.rsmjournals.com/cgi/reprint/34/1/91
Hood, R. Necropsy Procedures. In : Handbook of developmental toxicology. CRC Press; 1997 (p. 299) ISBN: 0-849-3013-51
My Feeder Euthanizer (DIY CO2 chamber) (2007) Retrieved March 19th, 2009, from Ball-Pythons.net Website: http://www.ball-pythons.net/forums/showthread.php?t=55509
National Research Council, Institute of Laboratory Animal Resources. (1996). Laboratory Animal Management: Rodents. National Academies Press. ISBN 0-309-0493-69
Podolsky, M. & Lukas, V. The Care and Feeding of an IACUC: The Organization and Management of an Institutional Animal Care and Use Committee. CRC Press; 1999. (p. 190) ISBN: 0-849-3258-03
Sibold, A., & Suckow, M. The Labratory Hamster & Gerbil. CRC Press; 1998. (p. 101) ISBN 0-849-3256-68
Sirois, M. Labratory Animal Medicine: Principles and Procedures. Elsevier Mosby; 2005. (pp. 84,112) ISBN: 0-32-3019-447
Sundberg, J. & Boggess, D. Necropsy Methods for Labratory Mice. In: Systematic Approach to Evaluation of Mouse Mutations (2000) (pp. 68-70). CRC Press ISBN 0-849-3190-56
Rollin, B. & Kesel, M. The Experimental Animal in Biomedical Research: A survey of scientific and ethical issues for investigators. CRC Press; 1990. (p.421) ISBN: 0-849-3498-18
UCSF LARC Newsletter. (2001) Retrieved April 19th, 2009, from IACUC.org Website: http://www.iacuc.ucsf.edu/New/MJ2001.pdf