I researched these rats online a bit before I got them. If I recall correctly, they have like 10 nipples which is the most amount of nipples in the rodent family. Common logic would tell me that that many nipples would accomodate for larger litters. I hear they are quite the nuisance in parts of africa as well.

My first litter was 12...not bad for a first litter...She didn't even eat any of them....

And talk about defending the babies... I can't even do cage maintenance (water bottle changings, feeding, cleaning) without being attacked by the parents. I don't see these animals becoming pets. They tend to nip and not sit still, they can really jump too. Imagine me cleaning out my 10 gallon, my cat and dogs watching intently, and then one rat jumps out of my "holding" bucket with a screen lid on top.....then the poor scared rat running across the room followed closely by the cat and then the two dogs, and then me....sigh. I have limited space at the moment but soon rat cleaning days will be in another room all together.