IACUC Policy: Toe and Tail Clipping for Identification of Mice    
Policy # IBT-206.00 IACUC Approval: February 27, 2014

This policy explains the mouse-toe and tail amputation methods of identifying mice in research.

This policy applies to all IACUC approved protocols subject to oversight by Texas A&M Health Science Center.

Principal Investigators (PI) have the responsibility to provide scientific justification to deviate from this policy.
The IACUC is responsible for ensuring all protocols meet this policy’s standard as a requirement for approval.

General Information:
Toe-clipping is a method for identification of small rodents that involves a numerical scheme in which the distal segment of certain toes is removed with a sharp instrument. It should be used only when no other individual identification method is feasible (such as ear notching, ear tags, tattooing, or subcutaneous implantation of a transponder identification chip) and if it is scientifically justified. According to The Guide for the Care and Use of Laboratory Animals ,"toe-clipping, as a method of identification for small rodents, should be used only when no other individual identification method is feasible and should be performed only on neonates. 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 (Castelhano-Carlos et al. 2010; Schaefer et al. 2010), 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 (Hankenson et al. 2008).

In the mouse, ossification of caudal (tail) vertebrae occurs between 2 and 4 weeks of age.  Prior to ossification, removal of the tail tip of a young mouse generally causes minimal pain. Tail tip sampling performed on mice >21 days of age is likely to cause more than momentary pain and distress as well as the potential for significant bleeding and requires anesthesia.


  1. 1.      Toe Clipping

1.1.   Toe clipping is acceptable for newborn pups up to 7 days of age. 

1.2.   Digit removal is limited to one toe per foot, two feet per animal (rear feet only).

1.3.   Limit amputation to the distal two phalanx.

1.4.   Any numbering system used should be designed to minimize the total number of toes clipped per animal, such as using the sex of the animal and coat color.

1.5.   Instruments (surgical scissors, scalpel blades, etc.) must be sterilized before use, protected 'from contamination between animals (such as placement on a sterile drape) and cleaned between animals.

1.6.   Hemostasis must be confirmed prior to returning animals to its cage. Animals should be observed for a minimum of 5 minutes after the procedure.

1.7.   A local anesthetic (e.g., lidocaine, bupivacaine, local anesthetic spray) must be used on the site of amputation

1.8.   Toe clipping is not considered a surgical procedure and does not require completion of the surgery attachment on the AUP.

1.9.   Alternative Identification Methods:

1.9.1.      Micro-chip

1.9.2.      Indelible markers

1.9.3.      Ear tags

1.9.4.      Tattooing

1.9.5.      Ear notching

1.9.6.      Toe nail clipping


  1. 2.      Tail clipping

2.1.   Tail tip removal should be performed at as young an age as possible.

2.2.   In mice <21 days of age, clipping of the tail can be performed without general anesthesia.

2.3.   In older mice (>21 days of age) general anesthesia is required.

2.4.   Tail clipping is not considered a surgical procedure and does not require completion of the surgery attachment on the AUP.

2.5.   Sampling must be performed using sharp, sterile scalpel blades or scissors.

2.6.   Instruments must be disinfected appropriately between animals.

2.7.   The smallest possible sections should be removed (3-5mm is recommended) but no more than one (1) cm may be taken at any age without the use of anesthesia.

2.8.   Repetitive sampling may be approved with total sections removed not exceeding one cm.  Repetitive sampling requires the use of anesthesia.

2.9.   Bleeding must be controlled by applying direct pressure to the wound or by the application of heat (cautery,) silver nitrate, or tissue adhesive.

2.10.                    The animal should be monitored until it is fully recovered from the procedure/anesthesia.

2.11.                    Investigators should be aware that tail ossification rates may be altered in genetically modified mice, and those animals should be monitored for the appearance of pain or distress following the tail snip.


Dagmar C Schaefer,Igor N Asner, Burkhardt Seifert, Kurt Burki, and Paolo Cinelli.  2010.  Analysis of physiological and behavioural parameters in mice after toe clipping as newborns. Lab Anim 44:7-13.
Hankenson FC, et al. Evaluation of Tail Biopsy Collection in Laboratory Mice.   JAALAS 2008 47:6 Pg 10-18. 
J Castelhano-Carlos, N Sousa, F Ohl, and V Baumans.2010. Identification methods in newborn C57BU6 mice: a developmental and behavioral evaluation.  Lab Anim 44:88-103. 

Version 00 – Initial Approval:  February 27, 2014