Kathy Heivilin, BS, CPIA, RBP
IACUC Vice Chair, Senior IACUC Manager
UM Biosafety Officer
Rodent Genotyping and Identification
Date Adopted: May 8, 2018
Last Review Date: January 15, 2021
The purpose of this document is to provide guidelines to researchers regarding acceptable methods for marking animals to identify individuals (e.g., ear punching) and tissue collection for the purpose of rodent genotyping.
The Institutional Animal Care and Use Committee (IACUC) must approve all methods for tissue collection prior to performing procedures on animals. Toe punching,
III. Ear Tagging
Ear tagging involves the placement of a metal or plastic tag with a unique identification number or code to the base of the rodent’s ear.
A. Animals must be 14 days or older.
B. Ear tags should be disinfected prior to placement.
C. The site should be disinfected prior to placement with chlorhexidine or 70%
D. Ear tags should be placed in the lower half of the ear to facilitate normal ear
position and on the outer third of the ear to avoid the area with the highest
E. Ear tags must be paced such that they do not cause a bend in the pinna,
interfere with the animal’s mobility, or be placed in such a manner that they can
catch on any part of the caging.
IV. Ear Punching and Notching
This method involves punching a hole or making a notch in the ear pinna. Commercial ear punches are available and inexpensive. Ear notch or punch tissue remnants can usually provide enough tissue for genotyping.
A. Animals must be14 days or older.
B. Ear punching or notching does not require the use of anesthetics or analgesics,
however, the animal must be appropriately restrained to ensure proper technique.
C. The ear punch device must be disinfected between animals. These devices can
V. Tail Clipping
This method involves amputating a very small segment of the distal tail. At < 21 days of age, the degree of ossification of the coccygeal vertebrate in the distal 5 mm is much less than that at 1 cm. After 21 days of age, the degree of ossification is similar along the entire length of the tail. The perception of pain is assumed to be more likely in bony vs. cartilaginous tissue. Therefore, tail clipping on mice or rats ≤ 21 days of age does not require anesthesia.
A. Animals must be appropriately restrained during the procedure to minimize
B. Sterile sharp scissors (must be disinfected between uses) or a sterile blade per
C. Only the distal 5 mm of the tail should be amputated.
D. Hemostasis can be achieved by using a silver nitrate stick, Quick Stop powder, or
by applying a gauze sponge over the site with gentle pressure until bleeding stops
E. Animals > 21 days of age or animals requiring a second tail sample must be
appropriately anesthetized using ketamine/xylazine, isoflurane, or a local
anesthetic during the procedure.
F. Animals > 35 days of age that require tail clipping must be anesthetized
(ketamine/xylazine, isoflurane, or local anesthetic) and
G. If multiple tail clippings are required a maximum of 1 cm total tail length may be
amputated, with all tail clippings combined.
VI. Toe Clipping
Toe clipping, as a method of identification of small rodents, should be used only when no other individual identification method is feasible and should be performed only altricial neonates and when combined with genotyping. The specific method(s) must be described in the Animal Use Protocol (AUP) and appropriate scientific justification provided. Under all circumstances, aseptic technique must be followed.
This method involves the removal of the distal phalangeal bone of one or more limbs. Toe clipping has the potential to induce pain and distress, and alter the animal’s gait and ability to feed.
A. Only one toe per foot may be removed.
B. Sterile sharp scissors can be used for this procedure (must be disinfected between
C. Hemostasis can be achieved using a silver nitrate stick, Quick Stop powder, or by
placing a gauze sponge over the site and applying gentle pressure until bleeding
D. Toe clipping may only be performed in mice ≤ 12 days and rats ≤ 7 days old.
VII. Other Methods of Identification
A. Micro Chipping: A small microchip transponder is injected subcutaneously
between the scapulae of the rodent. The
B. Micro-tattooing: A permanent mark using a needle and ink which is applied to the
tail, toes, or foot pads. The tattoo equipment must be disinfected between
C. Non-toxic markers: Sharpies can be used to mark the tail or fur of rodents,
however, the marks must be reapplied every 24 hours (or as needed) to ensure the
mark remains visible.
D. Animal Marker™ is another product available which can be used on rodent fur.
The Animal Marker™ can remain visible for 6 -12 weeks.
A. Guide for the Care and Use of Laboratory Animals, 8th
B. Hankenson FC Laire, Garzel LM, Fischer DD, Nolan B, and Hankenson KD.
Evaluation of tail biopsy collection in laboratory mice (Mus musculus):
Sci 47:10-18, 2008.
C. Vachon P. Anatomical and histological observations of fore- and hind limb toes in
adult mice after amputations performed at the age of two weeks. Can J Vet