JMO but I'd get rid of all those high white rats, there is no reason to take the chance and possibly breed babies who are going to suffer a horrible death. ESPECIALLY if you can't spot the signs of mega-colon and put them out of their misery ASAP. There have been lots of "breeders" who have tried to make the high white lines free from mega-colon, but they all give up cause they lose too many babies and don't bring their lines any further ahead.

If your just breeding them to immediately pop them in the freezer when their born, go for it, otherwise I'd feed those girls off/keep them as pets and get genetically better females for breeding