[Amtma Mousery]

I have noticed that a few of my does are having second litters soon after their first litter is almost weaned. However, during the time period, they do not come in contact with a buck. I do separate the young buck offspring at 4 weeks or when their testes begin to appear.

There is no chance of a rogue buck getting into their tanks. My only guess is that they have evolved superfetation. This phenomenon has occurred within multiple does in separate tanks and within different generations.

Has anyone else had experience with this behavior? TBH, it is becoming a nuisance because I wanted to breed some of these does to different bucks.

 

[Cheshire Gleam]

I haven't experienced exactly what you're describing though I do have one doe that had something similar going on with her. I checked on her in the morning, she was very large, likely going to give birth within the day, I came back from school and no kits were present, she was slim again. No mutilation or killing of her offspring had taken place to my knowledge as I couldn't find any remains, just some blood. I took her out of the nursery cage, assuming she'd cannibalized the litter, and put her in the bin with my nonbreeding does. Then a few days later, she was looking round and had a small amount of blood discharging from her vagina. I left her alone, she got huge again, and birthed a litter of eleven yesterday.

Not quite what is happening with your does, but mine was very clearly pregnant and showed the same signs of carrying, the first time without result and the second time successful, all within a month. Some of my mice, including this one, have your line incorporated into them so it's not too far from the realm of possibility. Have you left these does in with the buck they were mated to while she was giving birth? That could be your answer if yes. I've made this mistake and the doe has another litter around a week before the original litter is weaned. Maybe a doe you thought was female is really male? I'd hate to think certain mice have developed superfetation.