Collection of Tissues for Genotyping in Mice and Rats (IACUC)

The use of tail biopsy (also known as tail tip amputation, tail snip, or tailing) for genetic analysis of mice must be scientifically justified. Genotyping should be performed prior to wean (21 days in most strains).Anesthesia is required for tail biopsy in mice older than 31 days.

Background

Analysis of the DNA of individual mice is necessary for the identification of genetically modified animals that may serve as valuable models for research. The nature and quantity of mouse tissue required for this analysis are based on the type of DNA test being performed. While there are fewer strains of genetically modified rats that would require genotyping, methods studied and developed to be used for mice are appropriate since the developmental trajectory is similar (born altricial with 21 days to wean).

Since PCR requires amplification the gene of interest may be identified with a very small sample of DNA. Small volumes of peripheral blood, hair, saliva, ear punch biopsies, and tail biopsies are often sufficient for PCR testing. Solid tissue, such as tail or ear biopsy, provides the most consistent amplification to identify the presence or absence of a segment of DNA in an animal. The mouse tail biopsy procedure is the most commonly used procedure to obtain tissue for a PCR test.

In a young mouse less than or equal to 21 days of age, the tissue near the tip of the tail is soft and the bones have not completely mineralized. Therefore, amputation of the tail tip of a pre-wean mouse is presumed to cause only momentary pain for the animal.

As the mouse reaches 3–4 weeks of age, tail tissue maturation includes mineralization of the bone and increased vascularity. Tail tip amputation performed on an older animal is likely to cause more than momentary pain and must be done using appropriate anesthesia.

Guidelines

1. A tail biopsy for genetic analysis of mice may be performed only when scientifically justified. It is recommended that tail snips be performed at 12-17 days of age. DNA yield from tail snips is best from 10-21d of age. Negative mice can then be culled when mice are weaned at 21 days of age. If sufficient material for genotyping mice can be obtained from samples collected by less invasive methods, such as an ear biopsy, the less invasive or painful method is preferred. An ear punch biopsy has the advantage of offering simultaneous sampling and mouse identification. Ear punching should be performed after 12 days of age once the pinna is sufficiently large and appropriately oriented to accommodate the punch. Toe clipping is not a standard procedure and must be justified in the IACUC application form and performed before 8 days of age.
2. A tail biopsy in post-wean mice is a potentially painful procedure. While tail biopsy is recommended before weaning (21 days), anesthesia must be provided after 31 days.2 Because of this classification, the proposal to perform tail snips in mice over 21 days of age must be accompanied by a search for alternatives to this potentially painful procedure.
3. The total amount of tail tissue removed should be kept to the minimum required for the test to be performed. The excised length of tail should not exceed 5mm (normally 2mm is sufficient). Mice use their tails for thermoregulation and balance. The tail of the mouse is also an important site for research procedures such as blood collection, intravenous injection, and restraint.
4. Tail snips may be performed using a razor blade or sharp scissors. A razor blade is preferred. If scissors are used, they must be wiped clean with 70% ethanol between animals.
5. Hemostasis must be assured before returning the tail-snipped mouse to its cage. When tails are clipped at the recommended age of <21 days, hemostasis is easily achieved by direct manual pressure around the end of the tail. Light, direct pressure minimizes tissue damage and the subsequent risk of mouse-inflicted trauma to the tail end. Use of heat to cauterize the amputated end of the tail is discouraged. A medical-grade, nontoxic styptic powder may be used. Silver nitrate is toxic if ingested, so it is not recommended for this purpose as mice may ingest the agent. Application of a tourniquet to the tail of a mouse is strictly prohibited. Contact the veterinary staff for advice if problems with hemostasis are encountered or expected (e.g., mice with blood clotting disorders).
6. Repeated tail amputations on a single mouse are discouraged, but, if required, cumulative tail snips should not exceed 5mm of tail. If an additional sample from a mouse is expected to be needed at a later date, bisect the original tissue biopsy and preserve the extra piece at −20 to −80°C.

Recommended Procedures

Please follow these steps when performing tail snipping:

History

Effective Date: 05/10/2022
Next Review Date: 05/09/2025