A female rats oestrus cycle is usually every 4 to 5 days. When she goes in to heat it lasts about 12 hours. After mating the gestation period for a litter is anywhere from 21 to 23 days (21 being most common). If a male is living with the female during pregnancy he will need to be removed before the birth as the female can become pregnant almost immediately afterwards. Rat litters range in size from 6 or 7 babies up to 20. They can have anywhere from 4 to 7 litters a year. This means that if a mother rat had an average of 11 babies per litter, and had 6 litters in a year, she would have 66 babies in one year!
hope this helps

thanks for that. might be getting some rats soon then. how fast do they grow? from pup to adult size?

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1.1.0 royals
1.0.0 spider royal
0.1.0 mojave royal
1.0.0 het albino royal
1.1.0 CRB's
0.1.0 BCI
1.1.0 BD's
0.1.0 albino royal on the way