Sexing

It is possible to sex young rats at one day old, as the gap between the urethra and the anus is smaller in females than the gap between the penis and anus in males.

Female at four days old

Male at four days old

At 10 days old nipples will be visible on female rats. Males do not have nipples. As the fur grows this is more difficult to see.

Female at eleven days old

Male at ten days old

By three weeks old, most males will have obvious testicles. By five weeks, at which age the males need to be separated from their mother and sisters, it should be very obvious.

Adult female

Adult male

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