A bit back I picked up two very nice female rats. Both large in size and 6-7 months old. BIG girls. Neither of the girls have produced any offspring for me but have gone into several heat cycles and bred a few times? I haven't found anything unhealthy with them and they don't have a std either. Judging from their body they have bred before. My other girls are producing for me just fine. It's vague and I really would like to keep these two. They are the best temperments I've seen in a long time.