Question: Mice look quite similar. How can we distinguish them?

Answer: Mice can be individually numbered and marked for identification.

 

01. Numbering/Marking Methods
 

1) Ear Punching/Notching

Using a specialized ear punch to create holes or notches in the mouse's ears, or using scissors to make different notches on the ear edge for numbering.

● Principle: The left ear represents the tens digit, and the right ear represents the units digit.

● Right Ear (Units): A small punch on the inner ear edge represents 1, 2, 3; a single notch on the outer edge represents 4, 5, 6; double notches represent 7, 8, 9.

● Left Ear (Tens): The numbering rule is the same as for the right ear.

● Hundreds: A punch in the center of the right ear represents 100; the corresponding location on the left ear represents 200.

 

2) Ear Tagging

Using ear tag pliers to attach numbered ear tags (made of plastic, aluminum, or stainless steel) to the mouse's ear. The numbering range is typically 1~99999.

3) Fur Dyeing/Marking

Using a brush or cotton swab to apply chemical dye to different areas of the mouse's fur to create marks representing different numbers. Suitable for small numbers of mice and short-duration experiments.

● Principle: Apply marks from left to right, top to bottom.

● Numbering Scheme: Left forelimb = 1; left abdomen = 2; left hindlimb = 3; top of head = 4; mid-back = 5; base of tail = 6; right forelimb = 7; right abdomen = 8; right hindlimb = 9.

● For numbers >9: Two different colored dyes can be used interactively, with one color representing the units digit and the other the tens digit, allowing numbering up to 99.
 

 

Common Dyes:
 

● 3–5% Picric acid solution (yellow)

● 0.5% Neutral red solution (red)

● 2% Silver nitrate solution (brown)

4) Toe Clipping

Numbering is based on the location of toes clipped on the front paws (4 toes) and hind paws (5 toes) of newborn pups.

● Hind toes (left to right, ventral side facing the operator): 1, 2, 3... to 10.

● Front toes (left to right, ventral side facing the operator): 20, 30, 40... to 90.

● Important: This method is only suitable for pups aged 0-7 days. Avoid clipping more than two toes on a single paw of any mouse.

 

Question: How do we determine the sex of mice?
 

02. Sex Determination in Mice

1.  Anogenital Distance (AGD): Observe the distance between the anus and the genital papilla. In males, this distance is generally about twice that of females. (Primary method for pups aged 0~8 days).

 

2.  Hair between Anus and Genitalia: Females typically have a hairless line/area between the anus and genital papilla, whereas males have fur in this region.

 

3.  Nipple/Teat Presence: Female mice have visible nipples/teats; males do not.
 

 

References:

[1] Central South University Laboratory Animal Center.

[2] Kunming Primate Research Center, Chinese Academy of Sciences.

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