Which of the following is a permanent method for identifying laboratory mice?

• A. Visual fur color.
• B. Temporary ear tags.
• C. Tail numbering with ink.
• D. Ear punching and notching.

Answer: (D)

Permanent identification relies on a mark that remains with the animal for its entire life. Visual fur color isn’t reliable because coat color can change with strain, aging, or grooming and isn’t unique to an individual. Temporary ear tags can come loose or fall off, and markings on the tail with ink can fade as fur grows or wear off with handling. Ear punching and notching, however, create a physical alteration in the ear that persists through the animal’s life, providing a durable, readable identifier. This method is routinely used for long-term tracking in mouse colonies, with proper training and welfare measures to minimize pain and tissue damage.