how to sex a baby rat
Determine the sex of a rat as young as 10 days of age. Females will have small dots where the nipples will be and males will have a small bump where the testicles and penis will be located. Observe a rat's behavior. This will also help you to determine their sex though this is not a fool-proof method. Male rats tend to be quieter and more affectionate than female rats, although males may go through an aggressive stage when they enter adolescence at around six months of age.