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Postnatal development stages & sex determination in mice, FYI.

CowBoyWay

Cocked & Unlocked member
The postnatal development of a baby mouse...

A mouse is born naked with closed ears and eyes, and if a female, with a closed vagina.

Hair begins to appear at 2-4 days, ears open at 3-5 days, and eyes open at about 14 days.

Typically, the vagina opens at 24-28 days of age, but it can be delayed in some mice until they are 35-40 days old.

As soon as the eyes are fully functional, at about 16 days, pups will begin to eat solid food.

However, nursing can continue to at least the end of the third week and sometimes a week or more longer.

By the end of the third week of life, a young mouse resembles the adult in every aspect other than size and sexual differentiation.

Determination of sex
The sex of the newborn mouse can be determined from both the distance that separates the genital papilla and the anal opening, and from the general appearance of the urogenital-anal region.

The genital-anal distance in newborn males is generally 50% greater than in newborn females.

In addition, the male genitalia are often more prominent, and in the pre-scrotal region below, a dark pigmentation is often visible.

The simplest way to become adept at distinguishing gender is through pairwise comparisons of the pups — in each hand, a newborn pup can be held gently, but firmly, between the index finger and the thumb in an upside-down position.

As neonates age, gender determination becomes somewhat more difficult.

It becomes easier again at 8-10 days with the appearance of nipples along the ventral side of the female, and at the age of weaning (18-28 days), when the penis has developed more fully in the male.
:)
 
Nice stuff.

I am trying to breed mice again (for the 3rd frickin' time), and so far one seems to be pregnant (dont hold me to that). This should help me identify the younglings and seperate them accordingly, after they are weaned, of course.
 
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