Purpose

To provide guidance regarding effective euthanasia of mice and rats. Investigators should consult with the Attending Veterinarian (530-752-0514) for additional information, questions, or unique circumstances that may require deviation from these guidelines.

Background

Guidelines

The method of euthanasia must be an acceptable method as outlined in the 2007 AVMA Guidelines on Euthanasia. Scientific justification is required if conditional methods, including cervical dislocation and decapitation, are used on mice and rats over 14 days of age.

Euthanasia should be performed in procedure rooms or laboratory space away from other mice and rats, when possible. Death must be ensured prior to bagging the animal for disposal.

It is recommended that chemical methods of euthanasia (CO₂ chamber, inhalant anesthetics) be followed with a physical method (cervical dislocation, bilateral thoracotomy, or exsanguination) to ensure death.
 

1. Carbon dioxide
   A CO₂ chamber is the most commonly used method of euthanasia for small rodents. The chamber must allow visualization of the mice and rats during euthanasia. Proper technique must be followed to ensure a humane death, as CO₂ may have noxious properties. Place the mice or rats into a clean chamber that is not pre-charged with CO₂. Do not overcrowd the chamber; all mice or rats in the chamber must be able to make normal postural adjustments. Gradually increase the flow of CO₂ into the sealed chamber to minimize distress. For example, an appropriate flow rate is approximately 20% of the chamber volume per minute, or 6 psi. Leave the mice or rats in the chamber for 4-5 minutes until respiration has ceased. Remove the mice or rats and confirm the absence of respiration. A physical method (cervical dislocation, bilateral thoracotomy, exsanguination) may be used in conjunction with CO₂ to ensure death. Clean the chamber with disinfectant to remove all urine, feces and fur. Leave the chamber lid off to air out the residual amount of CO₂ in the chamber.

    

   
   

   CO₂ generated from dry ice is not an acceptable method of euthanasia.

   
   

2. Euthanasia of Mouse and Rat Fetuses and Neonates
   Neonatal rodents are resistant to the effects of CO2, therefore, alternative methods are required. (Mice and rats older than 14 days should be euthanized following the guidelines for adult rodents in the 2007 AVMA Guidelines on Euthanasia).
1. Fetuses
   

   Fetuses up to 14 days of gestation: Euthanasia of the dam or removal of the fetus results in rapid fetal death since fetuses cannot survive outside of the uterus.

   Fetuses from 15 days of gestation to birth: Decapitation with surgical scissors, hypothermia, or cervical dislocation are acceptable physical methods. An injection of a chemical anesthetic overdose is an acceptable chemical method.

2. Neonates
   

   Neonates up to 14 days of age: Injection of chemical anesthetics, decapitation, and cervical dislocation are acceptable methods of euthanasia. Hypothermia may be used as a method of euthanasia of altricial neonates provided they are less than 5 days old and they are not placed directly on the frozen surface (i.e., place them in a latex bag or cloth).

3. Animal Disposal
   After death has been ensured, place the mouse or rat carcasses in a disposable waterproof bag. Seal the bag and place the bagged carcasses in one of the barrels found inside the cold rooms or freezers designated for animal disposal.
   
   Mice and rats that are radioactive must be disposed according to the procedures stated in the PI’s Radioactive Use Authorization form. Mice and rats that are infectious must be disposed according to the procedures stated in the PI’s Biological Use Authorization form.

Procedure: IACUC-37
Date: Nov 16, 2006
Enabled By: the Guide, AVMA
Supersedes: Sept 30, 2004