Rodent Tagging and Identification

Animal tagging is a means to identify and distinguish all the individual animals of interest, which applies to wildlife, farm, or laboratory animals. It involves attaching a tag to a specific animal part that contains a unique identifier for each animal. The identifier can be numbers, alphabets, or a combination of both that distinguish and track the animals throughout their lifespans.

In rodents, tagging is the most popular identification approach. Typically, tags are made from metals and attached to the outer part of rodent ears, or the ear pinna. In rare circumstances, metal tags can also be attached to the rodent’s leg or tail.[1]

Figure 1: Rodent identification via ear tagging

Ear tagging in rodents is accomplished with the aid of an ear-tagging applicator. In laboratory settings, the ear tagging procedure proceeds as follows:[1-3]   

1. Sterilize the ear-tagging applicator, including the metal ear tags, if necessary. This can be accomplished using appropriate sterilization techniques.
2. Manually restrain the rodent, limiting its movement while making the ear accessible.
3. Wipe the surface of the ear where the tag will be placed.
4. Place the ear tag on the ear-tagging applicator, making sure that the hole at one end and the point at the other end are appropriately oriented. 
5. Position the ear-tagging applicator containing the ear tag to the middle lower part of the outer ear or the ear pinna. 
6. Align the ear tag to the distal one-third of the pinna, ventrally above the cartilage ring at the ear base.
7. Firmly and quickly squeeze the ear-tagging applicator. The ear tags are self-piercing and self-locking, and steady application ensures that the pain from the penetration is swift.   
8. Inspect the attached ear tag to ensure that it hangs appropriately from the bottom of the rodent ear. If it is misplaced, cut the ear tag using wire scissors.  

Once the ear tag is attached, routinely check for redness, swelling, or bleeding throughout the experimental period. Also look out for abnormal rodent behaviors such as excessive ear pulling or scratching, These are signs that indicate discomfort, inflammation, or infection arising from an inappropriate tag placement.

Apart from tagging, rodents can also be identified by creating temporary markings, microchip implantation, tattooing, and toe clipping. Like rodent tagging, these approaches can identify individual rodents and facilitate communication; however, they can be less advantageous.   

Figure 2: Rodent identification via microchip

In most cases, rodent ear tagging does not require anaesthesia, but ear tagging must be performed by trained animal technicians.[1]  

Rodent tagging supports regulatory compliance, which requires laboratories to provide good welfare and conduct ethical and humane animal care programs. 

In experiments and testing trials where rodents receive different treatments or patterns of manipulations, the identification of individual rodents is mandatory, along with maintaining contemporaneous health and medical records.[4] 

Similar to tagging, toe clipping and tattooing of the rodent’s tail or ear are permanent and require only a one-time application. Nevertheless, they are considered to be more traumatic. In particular, toe clipping is held as the least humane and should be avoided if not scientifically determined as irreplaceable.[1] 

In addition to being a humane method, rodent tagging simplifies individual rodent identification, which eases animal care and data collection in experiments or animal testing trials. Technicians, researchers, and veterinarians can rely on ear tags and promptly record observable variations within or across groups, along with any outlier.[1]

Laboratory animals are generally indistinguishable by eyes due to their highly homogeneous genetic backgrounds. Added to that, rodents are social animals, and laboratories typically keep them as colonies or treatment groups.[1]

Microchipping requires a scanner that reads the microchip implanted in each animal. Thus, it is more expensive than rodent tagging. It also adds a step in animal identification, which can be time-consuming and labor-intensive for large-scale experiments or testing trials.[1]

Temporary markings such as writing on tails and clipping or dyeing of furs are also considered the most humane identification approach that offers instant identification. The markings must be applied repeatedly, which leaves room for identification errors from human mistakes.[1,5]

Ear punching and notching are more permanent than markings. Still, identifiers on ear punches and notches can fade or change as the rodents heal or mature. They are also limited to one digit, and a second application will be necessary for a longer identifier.[1]

While rodent tagging can be highly advantageous, it is not applicable to every circumstance and still poses some limitations.  

For example, the size of a typical ear tag limits tagging to rodents in weanling stages and older or large rodents. Only personnel skilled in animal handling and aseptic techniques can apply ear tags. An inappropriate placement can cause the ear tag to fall off during the experiments. In severe cases, it can lead to inflammation or infection at the attachment site, causing discomfort or sickness that is deemed inhumane and disturbs the experiments or testing trials.[1-2] 

It is also important to note that metal tags can interfere with medical imaging techniques such as CT scanning or MRI. If similar techniques constitute a part of the designed experiments or testing protocols, consider adopting another rodent identification approach.[2]     

To dive deep into the advantages and disadvantages of each rodent identification approach, check out our article on Animal Identification Techniques.

Overall, rodent tagging provides an inexpensive and humane approach to instantly identify the individual animals in treatment groups of colonies. Rodents are not always put under when ear tags are applied; nonetheless, the procedure must be conducted by skilled and appropriately trained persons. 

Permanent ear tags facilitate and simplify regulatory compliance and data collection in large-scale and prolonged experiments and testing trials where the oversight of animals can be extensive, time-consuming, and prone to human errors. 

If you are looking for a durable and easy-to-use rodent tagging device, check out our Ear Tag Applicator!

1. Wang, L. “A primer on rodent identification methods” Lab Animals, 2005(34:4), pp. 64-67
2. Rodent Identification, IACUC Standard Procedure, Institutional Animal Care and Use Committee, Office of the Research, University of California, San Francisco, September 2021, 
3. Ear Tagging of Mice, Institutional Animal Care and Use Committee, Johns Hopkins University, July 2019, 
4. IACUC Policy 22:  Identification of Animals, Institutional Animal Care and Use Committee, Office of the Vice President for Research, Texas Tech University, December 2018, 
5. Burn, C.C., et al., “The Pen Is Milder Than the Blade: Identification Marking Mice Using Ink on the Tail Appears More Humane Than Ear-Punching Even with Local Anaesthetic” Animals, 2021(11), 1664.