why did my mouse die.

Question
I got home.  Went to check on my mice. They live in a small two level cage.  I noticed one of my females lieing on her side making weird small clicking noises.  She was cool to the touch and was like a rag doll also was like gasping for breath. About 30 min later she passed on.  I looked in the small hose i have for them and noticed my other female had died looked like she had been squashed up.  In the house they had dragged shredded newspaper in and made themselves cosy. My last remanding female is in perfect health.  Didn't seem like there was any fighting at all and they were all from the same litter.  Any suggestions as to what happened?

Answer
HI Jeremy,

It's impossible to guess how they died without a lot more information.  The gasping doesn't mean very much except that she was in pain, as mice dying is rarely pretty.  It's possible they developed a sudden respiratory problem, but more often than not respiratory diseases take a few days to kill a mouse (and you say you have one remaining mouse who looks healthy).  It's equally possible she was just having a tough time hanging on, unfortunately.

Usually females don't fight with each other, but there are always exceptions to the rule.  If she looked "squashed up" it may be that one of the other mice killed her if there were not enough resources, or if something else in their environment went wrong and triggered the aggression.  The other possible cause for her appearance is if she had been passed away for a few days - at which point their bodies begin to decompose and will look different.  Mice do not like having dead bodies in their cage, so the shredded newspaper may have been brought in after the first mouse passed away, as a sort of attempt at "burying" the mouse.

Check their cage - did they have food?  Water?  Did anything suddenly change in their environment?  For both of them to die so quickly would most likely mean fighting (since you have one remaining, healthy mouse, I would consider her), or a lack of resources.  The only way to be positive about what killed a mouse is a necropsy.  In the future you can call your veterinarian within the first 24 hours after an animal passes away and ask if they perform necropsies.  A simple necropsy will reveal obvious causes like trauma, fighting, large scale illnesses, etc.  You can sometimes pay extra to have histopathology done to look at tissues on a cellular level for more unique deaths - this will diagnose the weirder diseases that are not obvious on first glance.  With a necropsy you will usually not be allowed to take the animal back home for burial.

You might want to take your last mouse into your veterinarian to be sure she is healthy, just in case.  I'm sorry for your loss,

-Tam