Actually these are all breeders and we've currently had 6 litters with no megacolon. I got all but the siamese from Kara up at NERD and she's been breeding these lines (with new blood from time to time) for years with no problems so I feel pretty safe in saying that we won't have any major issues. I understand that there are issues with certain lines especially the black blaze and the high white but like I've said all of the females have had litters already with both of the males and we haven't seen any problems. I'm not saying that it will never happen but if it does that rat will be retired as a breeder.