Basic Biomethodology
For Laboratory Mice

It is important to select the appropriate identification method for your research purposes.

The method of identification selected must be described in the Animal Study Proposal.

Your choice of identification should be based on the age of the animal you wish to identify, the number of characters you wish to include and the duration of your experiment.

It is recommended that you record the identification information on the cage card in the event that clarification of the numbers or characters becomes necessary for any reason.

Indelible markers can be used for short-term identification.

Alternatively, ear punches, microchips, and tattooing are all permanent procedures.

Ear tags can be long-term, but there is always a chance they can become detached from the ear.

Consult your veterinarian if you have questions on selecting an appropriate identification method for your animals.

The NHGRI Guideline 01.3 "Identification Methods for Mice" can also be used as a reference.

Temporary Identification

Non-toxic, permanent markers can be used to temporarily mark the fur, tail or skin of the animal.

This ink, depending on the location, usually lasts 3 - 4 days without the need to remark.

Ear Punches

Different types of ear punches are available.

Ear punches should be sterile prior to initial use.

Extra ear punches should always be available, as they become dull with repeated use.

NHGRI uses the simplified system shown here, but there are many other numbering systems available that utilize both punches and notches.

To identify the mouse by ear punch, restrain it by the scruff using one of the methods demonstrated in the restraint section of this program.

The punch should be placed approximately 3 mm from the edge of the ear pinna.

If the punch is placed too close to the edge of the pinna, it is likely to tear and become difficult to read.

You should also be careful not to place the punch too far towards the inside of the ear to avoid injuring the animal.

The tissue removed with the ear punch can be used for genotyping.

Sanitize the ear punch between each cage of animals with 70% ethanol.

Using a chlorinated compound will cause the punch to become corroded.

Re-sterilize the instrument after use.

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Microchip Transponders

The microchip transponders are implanted subcutaneously between the scapulae for permanent identification of individual animals.

Each microchip is encrypted with a unique, non-replicable number.

The chips are read with a portable, hand-held scanner.

To implant these chips, the mouse must be briefly anesthetized.

The hair is removed from the insertion site by shaving or plucking.

The area is prepped with an iodophor, followed by alcohol.

The implantation needle, with the syringe attached, is purchased in a sterile package.

Make a tent from the loose skin at the implant site.

Insert the needle subcutaneously, with the bevel up, and depress the plunger.

Once the needle is removed, the injection site should be observed for bleeding.

If bleeding is noted, digital pressure with a sterile gauze pad should be applied.

If necessary, a drop of surgical glue can be applied to the needle entry site.

Tattooing

Tattooing can be used on both neonates and adults as a permanent method of identification.

Anesthesia is not required, but can be used, if necessary, to immobilize the animal.

There are two options available for tattooing at NHGRI.

One is the AIMS System, which consists of a tattoo machine that can be used to write numbers or other characters on the tails of adult mice.

It can also be used to tattoo the footpads of both neonatal and adult mice.

The use of tattoo equipment requires training beyond the scope of this course.

AIMS provides a course and certification program.

Consult your veterinarian or equipment manufacturer for further instructions on performing tattooing.

The Aramis tattoo system is a mechanical device that can be used to tattoo the footpads of adult or neonatal mice.

One example of a numbering scheme is shown below.

It is important to prevent potential cross contamination associated with the use of this equipment.

With the AIMS system, needles should be disinfected prior to use.

For the Aramis system, needles should be discarded after use. For both systems, excess ink should be discarded after use.

The tattoo apparatus and other supplies should be ethylene oxide sterilized, cold sterilized or steam sterilized before use between animal rooms.

Ear Tags

Ear tags are another means for identifying mice.

Ear tags can be imprinted by the manufacturer with several digits or letters.
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Special attention should be given to the proper placement of the ear tag.

Improperly placed ear tags can become easily detached from the ear.

The tags can also be torn out when the mice fight or may inadvertently become caught in the wire bar lid.

Restrain the mouse by the one or two-hand method.

Place a sterile ear tag into a sanitized ear tag applier.

Locate the proper position for placement.

For example, place the numbers in the upward configuration so that they can be easily read without restraining the animal.

Apply the tag to the base of the ear, approximately 3 mm from the edge of the ear pinna.

Do not apply the tag too close to the center of the ear. This may cause excessive inflammation, necessitating removal of the tag.

Do not apply the tag too close to the outer edge of the pinna.

This may cause the tag to become entangled with the foot of the animal or in the wire bar lid, causing it to become detached from the ear.

Toe clipping as a means of identification is not allowed at NHGRI.

Remember


• Select the most appropriate type of identification for your research purposes.
• The method of identification must be described in the Animal Study Proposal.
• Proper placement is essential for the use of ear punches or ear tags.
• Identification procedures should be initiated with sterile instruments. In addition, these instruments should be sanitized between cages of animals.
• Consult your veterinarian if you have questions on the selection or use of identificationu methods.