Guide to the Responsible Care & Use of Laboratory Animals at UWM

Chapter XIV:   Euthanasia Guidelines & Adoption/Procurement Program

Chapter XIV pdf format, Adobe Acrobat Required(for printing)

Euthanasia is the act of killing animals by methods inducing rapid unconsciousness and death without pain and distress. Pain can be defined as the perception that results from nerve impulses reaching the cerebral cortex. Therefore, the unconscious animal cannot experience pain. Rapidly occurring unconsciousness followed by respiratory and cardiac arrest is required for the method to be acceptable. At the conclusion of the euthanasia procedure, a follow-up exam should be performed to confirm the absence of a heartbeat. This can be done by feeling for a heartbeat, using a stethoscope, or by opening the chest.

Euthanasia methods should be consistent with the AVMA Guidelines on Euthanasia.pdf version, Adobe Acrobat required, June 2007 (Formerly Report of the AVMA Panel on Euthanasia), unless a deviation is justified for scientific or medical reasons. All methods of euthanasia should be reviewed and approved by the IACUC. When evaluating euthanasia methods for appropriateness some of the criteria that should be considered are the ability to induce loss of consciousness and death with no or only momentary pain, distress or anxiety; reliability; non-reversibility; time required to induce unconsciousness; species and age limitations; compatibility with research objectives; and safety of and emotional effect on personnel. The humanitarian requirements of the method should not be ignored in the urgency and/or need to obtain significant experimental results. Generally, inhalant or noninhalant chemical agents (such as barbiturates, non-explosive inhalant anesthetics and CO2) are preferable to physical methods (such as cervical dislocation, decapitation and use of a penetrating captive bolt). However, chemical agents may not be able to be used due to scientific requirements of the protocol.

Euthanasia may be necessary at the end of a protocol or as a means to alleviate pain or distress in animals. Protocols should include criteria for initiating euthanasia if necessary, such as degree of a physical or behavioral deficit or tumor size that will enable a decision to be made by investigator or veterinarian to ensure that the end point is humane and the goals of the protocol are met.

Euthanasia should be carried out in a manner that avoids animal distress. Sometimes vocalization and release of pheromones occur during induction of unconsciousness. Therefore, other animals should not be present when euthanasia is performed. Euthanasia should be performed by personnel who are skilled in methods for the species in question in a professional and compassionate manner. Persons performing euthanasia can receive instructions from the veterinarian, the principal investigator or the animal care supervisor. When delegating euthanasia responsibilities, supervisors should be aware that some employees or students may find euthanizing animals psychologically difficult.

  1. Modes and Methods

    Judging the humaneness of a particular euthanasia method can be extremely difficult for an uninformed observer. During the process of euthanasia, movements of an animal’s body (muscle contractions) do not necessarily indicate consciousness, nor does lack of movement in response to painful stimuli indicate the absence of pain (such as under the influence of curariform drugs)! There are three modes of action for euthanizing agents.

    1. Hypoxia/hypoxemia

    2. Direct depression of neurons
    3. Physical damage to brain (CNS) tissue

    The best choice depends on the use of the animal postmortem, safety to personnel, and the ethical considerations already discussed.

  2. Recommended Methods by Species

    1. Rodents

      1. Carbon Dioxide (CO2 chamber): CO2 rapidly acts by direct depression of the cerebral cortex. There are no changes in cellular structure, however, some involuntary muscle activity after unconsciousness may be noticed. There are chambers made for this purpose and CO2 tanks in the animal facilities. If dry ice is used animal contact must be avoided to prevent freezing or chilling. This is the preferred method under the proper conditions.

        Allow chamber to fill before placing animals in the chamber, close the lid and seal, begin CO2 administration by turning the valve of the CO2 tank. Allow the CO2 to flow for several minutes. Remove animals after 3 to 7 minutes. Be sure animals are dead before proper disposal. Eyes should be fixed and dilated.

      2. Inhalation Agent Overdose: (halothane, ether). These should be used under a fume hood. These agents should be stored appropriately in between use. Ether is irritating, flammable and explosive and should not be used in animal rooms. If ether is used, carcasses should be de-gassed in a fume hood for an appropriate time (i.e. up to several hours) so that carcasses are not explosive when disposed.
      3. Cervical Dislocation: (Used in mice and immature rats.) This technique causes direct depression of the brain. It may be distasteful to some due to violent muscle contractions that may follow. Data suggests that electrical activity in the brain persists for 13 seconds following cervical dislocation. Until additional information is available to better define the nature of the persistent EEG activity, this technique should be used only when scientifically justified by the user and approved by the IACUC if used without prior sedation or anesthesia. The tissues remain unaltered by chemicals. Those responsible for the use of this technique must determine that personnel who perform cervical dislocation techniques have been properly trained to do so.

        Grasp the animal by the tail with a pair of forceps or other suitable instrument and push down between the head and the shoulders. At the same time pull back on the tail until the cervical spine is dislocated.

      4. Decapitation: This is to be used with small rodents only. The animal should be sedated or lightly anesthetized first, since existing data suggests that animals remain conscious for 13 to 14 seconds following decapitation. If the technique must be performed without sedation or anesthesia, scientific justification must be provided and approved by the IACUC. There are few tissues that change with this technique.
      5. Injectable euthanasia solution: (Barbiturates) this works quickly in all species by depressing CNS functioning beginning in the cerebral cortex and moving to the respiratory center. Cardiac arrest quickly follows. Pentobarbital is the most frequently used barbiturate. It will cause drug residues and an enlarged spleen. Aesthetically it is considered more acceptable due to the general anesthesia first. A disadvantage is that the DEA requires strict accounting of all drug use.

        Obtain information regarding injectable euthanasia solution and dosage from the consulting veterinarian or drug formulary on web site. Inject rodents intraperitoneally or by cardiac puncture.

      6. Exsanguination: must be performed with prior anesthesia.

    2. Rabbits

      1. Carbon Dioxide (CO2 chamber): CO2 acts rapidly by direct depression of the cerebral cortex. There are no changes in cellular structure, however, some involuntary muscle activity after unconsciousness may be noticed. There are chambers made for this purpose and CO2 tanks in the animal facilities.

        Larger animals such as rabbits, cats and swine appear to be more distressed by CO2 euthanasia and therefore other methods of euthanasia are preferable.

        Allow the chamber to fill before placing the animals in the chamber, close the lid and seal, begin CO2 administration by turning the valve of the CO2 tank. Allow the CO2 to flow for several minutes. Remove animals after an appropriate time to be sure they are dead.

      2. Injectable euthanasia solution: Obtain euthanasia solution and dosage information from the consulting veterinarian. Inject rabbits in the ear vein or by direct cardiac puncture. If cardiac puncture is used, it is recommended to first sedate or anesthetize the rabbit. Barbituates will cause tissue changes in the animal. Be sure that the heartbeat is absent before the animal is disposed.
      3. Exsanguination: Perform on anesthetized animals only.

    3. Birds

      Because of the bird’s high respiratory rate, an overdose of inhalant agents will work well, (i.e. ether, halothane.) Personnel, however, must take precautions when working with some of these agents. CO2 also works well, but birds may show some distress before losing consciousness. Barbituates may be given. These are given IV or IP, most often injected in the wing vein. Cervical dislocation and decapitation is conditionally acceptable in poultry and other small birds. When using physical methods, the personnel must be adequately trained and IACUC approval is warranted if prior sedation or anesthesia is not used.

    4. Fish

      An overdose of MS-222 in the water may be used to induce euthanasia. An overdose of anesthesia (MS-222) can be given followed by decapitation. Stunning (cranial concussion) followed by decapitation or some other physical method can be used. Barbiturate overdose can be used intravenously, intra-abdominally or intrapleuroperitineally.

    5. Amphibians and Reptiles

      Acceptable practices include overexposure to gaseous inhalant anesthetics such as halothane administered in a chamber or with a facemask. Carbon dioxide can be used for terrestrial animals. Some reptiles can stop or reduce their breathing for long periods without overt ill effects and may not die even after prolonged exposure of inhalants. Overdose with injectable barbiturates can also be used on amphibians. An overdose of MS-222 can be used in the water for amphibians. Most amphibians and reptiles can be euthanized by cranial concussion (stunning) followed by decapitation or some other physical method. If decapitation is used without prior stunning or anesthesia it should be followed by pithing of the brain. Severing the spinal cord behind the head by pithing is an effective method of killing some poikilotherms. Since death may not be immediate double pithing is recommended. Pithing of the spinal cord should be followed by decapitation and pithing of the brain or other appropriate procedure. Quick freezing of deeply anesthetized animals is acceptable.

  3. Animal Adoption/Procurement Program

    The animal program has an animal adoption/procurement program. The forms that need to be completed can be found on the animal care program’s webpage: http://www.safety.uwm.edu/ can be retrieved from the lab manager or veterinarian. The only animals suitable for adoption/procurement are those that have not received any potentially harmful substances. The veterinarian will examine the animals prior to their release. Information will be sent home to people adopting animals regarding their care.

Updated September 19, 2007 by SAK