Sexing

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Sexually mature mice and rats must be properly paired to breed

successfully.  A single male mouse may be included in an

enclosure with one or more female mice without difficulty.

Including more than one male mouse in this situation invites

fighting between them.  By contrast, more than one male and

female rat may be housed together for breeding purposes within

the same enclosure without aggressive displays.



Sexually mature male mice and rats usually exhibit a prominent

scrotum.  Sexually mature female mice and rats usually exhibit a

prominent double row of nipples.  Furthermore, the distance

between the rectal opening and the penis of the male is greater

than the distance between the rectal opening and the urinary

opening of the female in both mice and rats.