if you are getting a new colony of rats, do not be disappointed if they do not produce right away. even if you get adults, it may still take a little time for them to settle in before they start making rat babies. i noticed that whenever i bring in new breeding stock, the earliest pregnancies in the new rats come at least two months after getting them (that translates to at roughly a month before they start copulating).....
do not worry about not noticing the pregnant females. it will be very obvious when it's time to move them to their own birthing tubs.
