So I needed to clean out my feeder bin today, little background, I feed off all my males before 4 weeks to my ferrets and only keep females for feeders.
One of my feeder females is pregnant, very much so. I took every mouse out of the tank and sexed them twice, all females, including a couple in heat so I watched the tank and them for a while and didn't see any chasing/humping going on. None of the others look remotely pregnant. I haven't fed many off lately because my snake was fasting but I know the last couple feeders were female for sure because they were retired breeders.
The tank is glass with a mesh lid so I don't believe a loose male could be the culprit either. She's out of my last litter and is 2 months old which puts an early blooming sibling out of the running. I take the dad out before they are even born so that's out. I'm waiting to see if maybe she's not pregnant but ill, by the looks of her she should drop within a few days and I put her in her own tank to keep an eye on. I guess with any luck I will get an extra litter out of this but still very confused on how this occured.