I have a couple of accidental breeding stories. The first story involves the second pair of rats we owned. The first pair of rats we owned (2 boys adopted from a junior high dairy council experiment) passed away, and we missed the lil' guys so much we went to a pet store and bought another pair. We purchased what we were told by the pet store workers were a pair of brothers...but obviously they weren't, if I'm posting to this thread.

Eddie and Timmy got along just fine and we didn't have the experience to know that "Timmy" was a female until she'd already become pregnant. Timmy became Tina, and eventually had a litter of 14. Because she was no more than 7 weeks old when she had the litter, she was too young and small to be able to take care of them, and many of them were stillborn. I think that having such a large litter while so young also stunted her growth and caused some other sort of injury, since she didn't really grow after she had the babies and one of her back paws didn't function properly and she had trouble walking.

We tried to save who we could, but only 3 of the babies lived, 2 girls and a boy. We gave the boy away, and kept the baby girls in with their parents (the father having been neutered by this time), and felt very lucky when all of these rats lived to at least 2 years of age, and Tina became the longest-lived rat we've have to date (she lived 3 years).
The second story involves a rat we adopted a few months ago. My mother works at a high school, and in late January one of the students thought it would be "funny" to buy a rat at a pet store and drop it in the school courtyard to scare people.

Fortunately, one of the teachers saw the kid do it and we were able to promptly rescue the poor thing (who we later found out hadn't been fed or given water in almost a day, since she was "just for a prank"). Mom adopted the rat (who we named Nezumina), and she was rather nippy for a while, which for a while we chalked up to her having such a bad experience. After a few more days we realized she was pregnant and, sure enough, about 9 days after we took her in she had a whopping 16-baby litter, all of which survived. I think we were very fortunate that Mina turned out to be such a great mother, as she couldn't have been more than 3 months old when she had the litter and all of the babies survived (12 boys and 4 girls). We were able to find homes for 9 of the boys, but ended up keeping 3 boys and all the baby girls. The babies are about 4 months old now and so far, so good, but we're all expecting there to be some sort of health problems, as the prankster who bought the rat didn't think about the long-term for the rat and probably just got a cheap feeder.
I'd never planned on breeding rats anyway, and having these experiences really reinforced that view. I think breeding is something best left to the experts, to people who specialize with rats, unlike a lot of pet stores who don't have the knowledge and/or experience to deal with breeding rats properly. We're being ultra-ultra-careful with our boys and girls so we don't have any more unexpected litters...we love our ratties, but I know how hard it would be to deal with more litters.

We've been pretty lucky so far with the way our accidental litters have turned out, but we're definitely not planning on having more.
