I put my groups together at 12 weeks old and they have their first litters when they are ready.
I average 13 to 15 babies on 2nd litters with some smaller litters of 8 to 10 by first time moms.

One of my elder ratties, he's about 600 grams


One of my 5 week old black velveteen dwarfs.


The varieties in rats is amazing.