Ming, the experiment is finished. How should mice be euthanized? What are the methods?

 

The goal of euthanasia is to end an animal's life in the most humane way possible, minimizing pain, fear, and distress. It ensures loss of consciousness and pain perception in the shortest time. Let's discuss the relevant knowledge in detail.

 

Common Euthanasia Methods for Mice
 

Euthanasia in scientific applications, teaching, and research may be appropriate under the following circumstances:

1.  At the conclusion of an experiment.

2.  To obtain blood, tissues, or organs required for the study.

3.  When animal pain or distress exceeds the anticipated severity.

4.  For reasons of animal health and welfare.

5.  When animals are unsuitable for continued breeding (e.g., breeding-related factors).

 

Methods
 

I. Carbon Dioxide (CO₂)

Carbon Dioxide (CO₂) is a commonly used gas for euthanasia. When mice inhale 40% CO₂, they quickly enter an anesthetic state. Prolonged exposure leads to death.

● Advantages: Relatively simple to perform, and it can quickly and effectively render animals unconscious.

● Procedure: Place animals in the chamber and secure the lid. Connect the CO₂ tubing to the inlet (often the water bottle port). Open the gas cylinder valve and fill the chamber with CO₂ at a rate that displaces 10-30% of the chamber volume per minute. Allow CO₂ to fill the chamber. Once mice are recumbent and have lost motor ability, the flow rate can be increased slightly. The maximum flow should not exceed 0.5 kPa. Confirm death by checking for absence of movement, breathing, and pupillary dilation. After turning off the CO₂, observe for an additional two minutes to confirm death.

● Precautions: Mice should be in an appropriate container (e.g., IVC cage). Animal density should not be too high. Do not pre-fill the euthanasia chamber with CO₂ before placing the animals inside.

 

II. Injectable Agents
 

Common injectable agents include barbiturates, potassium chloride, etc. Air injection can also be used to cause rapid, painless death. This method is suitable for various experimental scenarios, especially when the intact animal body is required.

Common injection routes include intravenous (IV), intraperitoneal (IP), and intracardiac (IC). IV injection is preferred. IP injection requires a higher dose, which may prolong the time to death and cause pre-death struggling. IC injection is only appropriate for animals that are moribund, in shock, or deeply anesthetized.
 

(Image source: The Laboratory Mouse (Handbook of Experimental Animals))

Physical Methods
 

Sedatives may be administered before physical methods to reduce animal distress. For methods involving exsanguination or terminal blood collection, anesthesia should be administered first.
 

III. Cervical Dislocation
 

Cervical dislocation involves applying force to disconnect the spinal cord from the brain, resulting in rapid, painless death. It is suitable for mice weighing less than 200g.

● Advantages: Rapid loss of consciousness, minimized pain, simple to perform, and leaves internal organs undamaged.

● Procedure: Secure the mouse on the cage lid. Grasp the tail with one hand and lift the mouse at approximately a 30-degree angle. Quickly and firmly press down on the mouse's head with the thumb and forefinger of the other hand.
 

(Image source: Laboratory Animal Center, Sun Yat-sen University)

IV. Decapitation
 

Suitable for mice under 14 days old. A guillotine or sharp scissors are used to rapidly sever the medulla oblongata, separating the head from the body. Consciousness is lost within 5-30 seconds.

● Advantage: Ensures tissues or body fluids are free from chemical agent interference. It can also provide intact brain tissue for research.

 

References:

[1] Chinese University of Hong Kong - Laboratory Animal Centre

[2] Sun Yat-sen University (Shenzhen) - Laboratory Animal Centre

[3] Zhejiang University - Laboratory Animal Centre

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