Varieties of acceptable and recognized methods are available for individually identifying research animals. These include, but are not limited to, ear tags/notches, tattoos, sutured beads, subcutaneous transponders, colored stains, dyes, and freeze brands. The Guide for the Care and Use of Laboratory Animals states “As a method of identification of small rodents, toe-clipping should be used only when no other individual identification is feasible. It may be the preferred method for neonatal mice up to 7 days of age as it appears to have few adverse effects on behavior and well being at this age, especially if toe clipping and genotyping can be combined. Under all circumstances, aseptic practices should be followed. Use of anesthesia or analgesia should be commensurate with the age of the animals.”
Toe clipping is the removal of the last phalangeal (toe) bone of a digit from one or more limbs. It is usually done for the purpose of identification and genotyping of animals. The Food and Drug Administration also discourages the use of toe clipping as a means of animal identification. The UCHC Institutional Animal Care and Use Committee (IACUC) typically does not approve the use of toe clipping when performed only for the purposes of identification.
The Interagency Research Animal Committee considers toe clipping to be a painful procedure; however, it may be done only after IACUC approval with proper justification:
a) Toe clipping is done for unique and highly individualized animal identification that is permanent and unambiguous and is used for the long-term identification of potential breeding mice;
b) If the neonates need to be identified before day 7, toe clip is preferred;
c) If the same animal must be genotyped, then the animal may only undergo one procedure for both tissue harvest or genotype and permanent identification;
d) When no other individual identification method is feasible (such as ear notching, ear tags, tatooing, or subcutaneous implantation of a transponder identification chip);
e) Toe clipping for the sole purpose of obtaining DNA is not acceptable; and
f) The toe clip procedure should be detailed in the IACUC protocol.
1. Toe clipping can be performed on pups up to 12 days of age; the preferred age is less than 8 days of age. Toes may be removed without anesthesia on mice up to 8 days of age. Toes must be removed with anesthesia on mice 8 days of age or animals whose eyes have opened and appropriate post-operative analgesics must be used.
2. The procedure should be performed with sharp, disinfected scissors. Scissors must be disinfected between animals. Research presonnel should confirm that there is no bleeding prior to returning the animal to its cage.
3. Toe clipping is limited to no more than one per foot.
4. Since the rodents hold food with their forepaws, the IACUC will only allow this procedure on hind paws, one toe per paw, and permits the removal of just the first bone.
5. The procedure is not recommended for rodents used in psychology research as it may affect the gait or grip strength of the animal.
1. The Guide for the Care and Use of Laboratory Animals. National Research Council, National Academy Press, 2011.
2. IACUC Guidebook, 2nd Edition, NIH, Office of Laboratory Animal Welfare, 2002.
3. Good Laboratory Practice Regulations; Minor Amendment, Federal Register, VOl. 54, N. 75, 1989. (www.nal.usda.gov/awic/legislat/fdaclip.htm)
4. National Institutes of Health, ARAC, Guidelines for Toe Clipping of Rodents, Revised 5/12/04. (http://oacu.od.nih.gov/ARAC/).
Effective Dates: June 17, 2021 through June 30, 2024