I'm sorry to hear of your mouse. It sounds very much like what I had. Mouse fine one day, skinny and dead the next.
I spent an entire night researching the symptoms and I found out mine had megacolon. A dreadful and terribly painful disease of the digestive tract. It's a genetic disease that is on the same gene as color, so it's often referred to as the "white streak" or "piebald" disease.
Megacolon is where the where the nerves that control the normal muscle contractions of the colon fail to work, and food builds up. It's usually obvious around the 6th week of life when they're beginning to get the majority of their diet from solid food.
When the two that I had died, I did a haphazard internal exam and their stomach and large intestine were so compacted it was hard as a rock, literally.
One thing I did notice on both of them was:
- Both were bi-colored and had more white than the other color present.
- The colonies they were in, both had powdered food in the bowl. Normally as the blocks are eaten, there isn't much left. But since they couldn't fit anything in, all they were able to do was chew the food up and spit it out.
The male that fathered these two was eaten a couple of weeks later by a wild snake. So hopefully I've contained the problem. I may have a few more incidences pop up, but hopefully I can monitor which female they came from and rotate her out of the breeding pool altogether.
Here's a really good website I found from the search I did a while back:
http://ratguide.com/health/digestive/megacolon.php
I hope that helps. It says that affected individuals can be nursed through their lives with special diets and enemas. But what quality of life is that for a rodent? I would suggest immediate euthanasia for those mice found to be afflicted.
The first picture of the mouse on her back looks to me like it clearly shows the outline of the stomach, that lump just down from where the rib cage ends.
Were the father and mother of the baby related? If so, I would consider converting your male into a feeder and buying a totally unrelated male mouse. That would be a quick fix for the moment. Cause if it popped up that early in the game, I'd almost bet your male and female are brother and sister. That's where I got mine, the male was bred back to his daughter. But since there were 3 of his daughters in his colony, I don't know which one it was. But its all worked out now for the time being. But you've got the gene floating around now, so you're going to have it crop up if you're not careful about who you breed to who.
Hopefully you didn't drown her (quick survey of the background). A quick flick to the head is much better, all over in an instant and no panic beforehand.
