We recently purchased a very pregnant mouse from a LPS. She delivered within hours of getting her home. She had 10 babies and all seemed to be doing well, fat, nice pink color. Mom was feeding them well and tending to them just fine. Just before they reached hopper size I noticed the babies started dying off (quickly). As I was pulling out the dead ones, I noticed the live babies had pus oozing out of their rectums... within a day the rest died.

We did not feed them to any snakes.

I'm guessing infection was the reason for the pus, but why would they make it to this stage and then suddenly all die off so fast? Mom still seems healthy, normal poop, appetite, activity, etc.

Should we breed her again or cull her?

They were kept in a 20 L, on wood pellets with shredded newspaper for nesting. Feeding RodentPro lab blocks.