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Collecting Samples for Genomic Analysis from Genetically Engineered Mice & Rats


In order to comply with government regulations governing the use of vertebrate animals and to ensure the well-being of animals at UConn Health, the Institutional Animal Care and Use Committee (IACUC) has implemented a policy regarding the collection of samples for genomic analysis from genetically engineered mice and rats.


To determine if genetically-engineered mice and rats carry a gene of interest, tail biopsies are commonly performed to obtain samples for DNA analysis. DNA for polymerase chain reaction (PCR) analysis can also be obtained from ear punches during identification procedures, blood samples, or saliva swabs. To obtain larger amounts of DNA for Southern Blot testing, tail biopsy is usually performed. Tail biopsy is a safe and humane procedure when it is performed correctly.

Tail Biopsy:

Tail biopsy is recommended to be performed between 10-21 day old mice as the tissue is soft, and the bones have not yet been calcified.  Further, the yield of DNA is the highest.

Procedure for Mice and Rats Between 10 and 21 Days of Age (or at weaning)

1. The tail biopsy procedure should be described in the approved animal care and use protocol.

2. At this age, the tail is still soft and the tail vertebrae have not yet calcified.

3. Local anesthetics are recommended, but not required.

4. Plastic restrainers are useful to hold the mouse.

5. The tail biopsy procedure must be performed using clean gloves and a sterile sharp scalpel, sharp scissors, or razor blade.

6. Prior to biopsy, the tip of the tail may be numbed with ice or immersed in ice-cold isopropyl alcohol for 10 seconds.

7. Do not use iodine solutions because they may interfere with DNA analysis.

8. Tail skin should be disinfected with alcohol prior to incising the tip. Make one clean cut through the tail. The length of the biopsy cannot exceed 5mm.

9. Following the biopsy procedure, bleeding should be controlled using local pressure. After releasing the animal back into the cage, it should be observed to make certain that the bleeding has stopped. The presence of blood in the cage may cause aggression between cagemates.

10. If bleeding occurs, it may be necessary to cauterize the tip of the tail with silver nitrate.

11. Please consult the Attending Veterinarian for advice when using cauterizing agents, as they may be toxic if they are ingested by the animal.

Procedure for Mice Older than 21 Days of Age

1. The procedure should be described in the approved animal care and use protocol. The rationale for testing older mice should be explained.

2. The use of a general or local anesthetic is required. Appropriate local anesthetics can include EMLA or lidocaine cream. Appropriate general anesthetics can include ketamine/xylazine, ketamine/medetomidine, or isoflurane.

3. Please consult the surgery guidelines for general anesthetic details.

4. Steps 5 to 10 should be followed as described above.

5. For rats > 35 days of age, the use of a general anesthetic is required.

Note: Removal of more than 5 mm of tail in rodents is only allowed in exceptional cases, and it must be approved by the IACUC. If repeat sampling is necessary, anesthesia must be used and only small amounts of tissue may be taken.

Ear Biopsy/Punch:

1. It can be done during the ear punch identification procedure.

2. The ear punching technique does not require anesthesia if performed by skilled staff. The appropriate time for ear punch is between 15 and 17 days of age.

3. The animals should be manually restrained and the sample should be collected aseptically.

4. Bleeding after an ear punch is uncommon and the animal can be released directly into the cage.


1. Blickman, A. and C. Vogelweid. ISUM IACUC Guidelines, February, 2003.

2. The Guide for the Care and Use of Laboratory Animals. National Research Council, 2010.

3. Tissue Collection for Genetic Identification of Rodents. Division of Laboratory Animal Resources, University of Kentucky Medical Center.

Effective Dates:  June 2, 2022 through June 30, 2025