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Institutional Animal Care and Use Committee Policy on Murine Tail Tip Biopsy


The purpose of this policy is to provide guidance to animal users that would like to obtain genomic samples from murine tail tissues (tail biopsy). Tail tip biopsies are a conventional procedure for genotyping transgenic animals.  From this tissue, genomic DNA is extracted to ascertain the presence or absence of a specific transgene using PCR or other DNA analysis techniques. Tail biopsy is safe and humane when performed correctly. This policy describes the requirements and restrictions for protocols that request murine tail tip biopsy procedures and provides consistency during IACUC protocol review.


  1. All tail biopsies procedures should be included in an approved Animal Care and Use Protocol.         Note: Modifications to this protocol can be made with scientific justification and IACUC approval.
  2. In mice less than 21 days of age, tail tip biopsy may be performed without use of analgesia or anesthesia.  The ideal age is 12-14 days old.  This will allow identification prior to weaning and more efficient use of cage space.The timing of the biopsy is important because a rodent’s terminal vertebrae ossify between 2 and 3 weeks of age. It has been noted that there is no increase in DNA quantity with increased age as the rapidly growing tail tip contains more DNA than bone.  Biopsies performed on animals greater than 21 days of age are likely to involve more than momentary pain and distress, as well as the potential for significant hemorrhage.  Scientific justification is needed in order to allow this procedure on older mice.
  3. A minimum amount of tissue required for analysis should be obtained, with 5mm (0.5 cm) being the maximum allowed. Tail tip biopsies are limited to a maximum of 2 times because the tail is important in body temperature control and balance in rodents.
  4. Murine tail tip biopsies should be conducted using sterile, sharp instruments such as a stainless steel surgical blade or sharp scissor. The instruments should be decontaminated between animals with 70% Isopropyl alcohol or an appropriate disinfecting agent such as Nolvasan (chlorhexide diacetate). If a chemical disinfectant is used, the instrument must be rinsed with sterile water or saline between animals.  Alternately, instruments can be heat sterilized using a hot bead sterilizer or flame. The instrument must be changed when dullness of the cutting edge is noted.
  5. After tail tip removal, the biopsy site must be observed for active bleeding.  Hemostasis must be achieved before returning the animal to the home cage. Digital pressure, cautery, tissue adhesives, coagulation powder or coagulation sticks (i.e., silver nitrate) may be used to achieve hemostasis.

Deviations from this protocol:

***If you are using mice OLDER than 21 days or larger mice (over 50grams), specific justification and approval from the IACUC must be obtained.** In these cases, appropriate local analgesia or general anesthetics must be used.


Summary of Important Restrictions

  • No more than 5mm (0.5 cm) of tail tissue may be removed from any one animal during a biopsy procedure.
  • No more than two tail biopsies are permitted per animal.
  • Animals should not be returned to their home cage until hemostasis and complete recovery from anesthesia has been obtained. Hypothermia should be prevented at all times during the procedure.


Personnel in the Office of Laboratory Animal Care can assist and train personnel in the above techniques.

**Extreme circumstances that would allow tail biopsy from 21-25 days without the use of analgesics and/or anesthetics are defined as lines of animals whose offspring exhibit a failure to thrive, have developmental or growth delays, or a genetically induced disorder that causes fragile health. These extreme circumstances must be described in the original protocol or must be approved as an amendment to the protocol. The IACUC must review and approve the extreme circumstances prior to the performance of the tail tip biopsy.

Portions of this SOP were modified in reference to policies from U. Wisconsin, Madison, Duke University, U. Michigan, UCSF.


IACUC approved and modified:  December 3, 2013