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Home : Euthanasia : Rodents

Rodent Euthanasia

CO2

Considered an acceptable euthanasia agent for laboratory rodents when properly administered.

The NIH Office of Laboratory Animal Welfare (OLAW) recently issued a Public Health Service Policy guidance clarifying current requirements for the use of CO2 as a euthanasia agent. The acceptability of CO2 as a euthanasia agent is predicated on the following:

  • High concentrations of CO2 may be distressful to some species. Accordingly, pre-filling of the CO2 chamber is recommended only under circumstances in which such use has not been shown to cause distress.
  • Death must be verified after euthanasia and prior to disposal.
  • All individuals administering CO2 euthanasia must be appropriately qualified and monitored. IACUC-approved protocols and institutional policies regarding CO2 euthanasia must be followed.
  • Euthanasia chambers must not be overcrowded. Mixing unfamiliar or incompatible animals in the same container may be distressful.
  • Compressed CO2 in cylinders is the only AVMA Panel-recommended source of CO2 for euthanasia purposes.

Advantages:

  • Provides rapid depression and anesthesia (CO2 narcosis).
  • Non-flammable and non-explosive.
  • No chemical residues are introduced into tissues.
  • It does not result in distortion of cellular architecture.

Disadvantages:

  • CO2 is heavier than air. Incomplete filling of the chamber can induce some animals to avoid exposure by climbing or jumping which appears distressful.
  • CO2 may be distressful to some animals due to irritation of the mucous membranes of the respiratory tract and stimulation of respiratory centers in the brain. The AVMA panel considers the degree of distress to be mild and unlikely that it is more unpleasant then inhalation of volatile anesthetics.

Neonatal rodents are resistant to CO2 induced euthanasia. Euthanasia of neonatal rodents is discussed below.

Recommendation:

  • At PSU, CO2 is the preferred method of euthanasia for rodents. CO2 tanks with euthanasia chambers are located in many of the procedure rooms as well as in the necropsy room. Dry ice may not be used to generate CO2 for euthanasia.
  • Gas flow should be maintained for at least one minute after apparent clinical death (cessation of respiration). If an animal is not dead, CO2 narcosis must be followed with another method of euthanasia.
  • To insure that unintended recovery does not occur after CO2 exposure, cervical dislocation may be performed or a stab incision may be made (between the ribs) into the chest cavity on both sides of the animal.

Volatile Inhalant Anesthetics

  • Animals are placed in a sealed container such as a bell jar containing gauze soaked with the anesthetic agent.
  • Animals should be separated from the anesthetic soaked gauze by a false bottom or other method to prevent direct animal contact with the liquid anesthetic.
  • A number of volatile inhalant anesthetics may be used for anesthesia. Contact an ARP veterinarian for information regarding the use of volatile inhalant anesthetics for euthanasia.
  • All volatile inhalant anesthetics require some method of scavenging the waste anesthetic vapors (i.e., working in a biosafety cabinet).

Cervical Dislocation

  • Acceptable under the following conditions:
  • Cervical dislocation should be performed on sedated or unconscious rodents.
  • Investigators are responsible to determine that personnel using cervical dislocation are properly trained to do so. ARP will provide training to those who request it.
  • Cervical dislocation on conscious rodents requires scientific justification and prior approval by the IACUC.

Advantages:

  • Induces rapid unconsciousness.
  • Does not chemically contaminate tissue.
  • A quick procedure.

Disadvantages:

  • Aesthetically unpleasant for personnel.
  • Physical damage to tissues and structures in the cervical area along with bleeding may interfere with sample collection.
  • When performed incorrectly it may induce or prolong animal suffering.

Barbiturates

  • Acceptable
  • Barbiturates may be injected intraperitoneally to euthanize rodents.
  • Agents available for use include sodium pentobarbital and pentobarbital combinations.
  • Barbiturate drugs must be used under the supervision of personnel registered with the United States Drug Enforcement Administration (DEA).
  • Requires strict accounting of quantities used.
  • Requires locked storage.

Disadvantages:

  • Contamination of tissues by chemical residue
  • Slow when administered by intraperitoneal injection.

Exsanguination

  • May only be used to as an adjunctive method to euthanize unconscious animals.

Neonatal Rodents

  • The AVMA panel does not provide specific guidelines for the euthanasia of neonatal rodents.
  • Neonatal rodents up to 10 days of age are resistant to euthanasia with CO2.
  • The following recommendation is based on information contained in Recommendations for Euthanasia of Experimental Animals: Parts 1 and 2. Laboratory Animals (1996) 30, 293-316 and (1997) 31, 1-32.
  • Although neonates are resistant to volatile anesthetics and CO2, prolonged exposure will induce anesthesia. Exposure to CO2 or volatile anesthetics such as ether and isoflurane should not be relied on as the sole method of euthanasia for neonates. It should be followed by decapitation.

Recommendation

  • Place neonates in a plastic bag from which all air has been purged. Fill the bag with CO2, seal the bag and observe periodically until all signs of respiration and movement are gone (this may take from 5 to 10 minutes). Neonates should be decapitated after this period to insure death.