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Mice/weight loss


I have three female fancy mice that I have had approximately 8 months. I recently noticed that one of them appears to have lost weight; she looks extra skinny just above her back legs. She's a little lethargic, but doesn't appear to be exhibiting any other symptoms (no sneezing, clear eyes, no diarrhea, etc.). The other two mice seem fine. Since I don't know exactly how old she is, I was wondering if this could possible be old age, or if I should be concerned about it being something else.


Hi Stephanie,

I've tried to come up with as many ways as possible to explain her weight loss here, but this is really just a list - depending on how drastic or sudden her condition is you may consider bringing her to a vet who works with pocket pets like mice.  This is always the quickest and best option if possible, since they will be able to look at her personally and help you figure it out.

Is she in the same cage as the other mice?  If not, I would check the water bottle first - dehydrated mice look like they have suddenly lost weight and sort of shrunken, if that makes sense.  Sometimes bottles get stuck, so a tap to the dropper will let you know if this might be a problem for her.

If she is in the same cage with the others and no one else is looking thinner, I would think something else is going on that may need attention.  Do you spot her eating, or is there any chance the other girls could be guarding their food?  If she isn't eating much it could be because she does not feel well - she could have a dental problem or something bothering her stomach.  There are a few potential gastrointestinal infections that could cause weight loss, but they would also cause a noticeable difference in her stool and all are highly contagious, so I would keep an eye on her bathroom habits and the condition of the others that live with her to figure out if she needs antibiotics.  A vet is the best person to determine what is causing her weight loss specifically and can get you the most appropriate treatment, but if you would like to try antibiotics and cannot find a suitable veterinarian, please feel free to write me a followup and I will get right back to you with some at-home instructions.

One other possibility is an internal tumor that is making her feel ill.  A mouse that feels bad will eat less and sleep more, and depending on where a tumor is located, it could cause stress on internal systems or poor absorbing of nutrients.  This isn't necessarily likely, but it is one possibility for unexplained weight loss and can have both genetic and age factors.  There isn't very much that can or needs to be done for a tumor, however, so the best option is to provide high quality and high protein foods - both cat kibble and scrambled eggs made with water instead of milk are very high in protein and make great treats to help her pack on some weight.

Lastly, she could simply be stressed or depressed.  If she gets along well with the others, don't separate her, but if they tend to chase her a lot or give her a hard time you might try giving her her own space for a bit.  This will also help in case she does have an illness.  You can also try introducing new toys and things to climb on to encourage her to get active.  If it is colder or warmer than usual in their environment, try gently adjusting the climate or cage to keep it more consistent with their usual.

I hope I helped explain the possibilities, and hopefully I did not make it sound too scary!  The fact that she has no other symptoms is really wonderful, and a great sign.  If you notice any other details that might help narrow it down, or if she suddenly loses more weight or body condition, please consider bringing her to a vet as soon as possible.



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I can answer questions regarding mice as pets, mouse behavior, color and coat genetics, breeding techniques, and general health questions. I can help with caging and setup, nutrition, social issues, and what to do in most mouse emergencies (such as unplanned litters, injuries, fighting, etc.). I can also assist with questions pertaining to orphaned mouse pups, weaning litters, and questions of mating and birthing. I cannot answer questions about exotic or wild varieties of mice such as spiny or pygmy mice. *****FOR EMERGENCIES, anything requiring immediate medical intervention, PLEASE take your mouse to a professional veterinarian or wildlife rehabilitator who works with mice as soon as possible! IMPORTANT RESOURCES: Raising Orphaned Mice: Orphaned Mice Videos: Natasha's Your First Mouse: General Mouse Help: Mouse Info and Exotic Breeds:


I have enjoyed the companionship of mice nonstop since 2004, and spent a year caring for them in a lab where I learned a great deal about their breeding, social needs, and health. I spent a few years breeding them, specifically working with albinos, marked mice, angora mice, and satins. My education never stopped - I am learning something new every day from current and well-established research thanks to the wonderful folks at the Jackson Laboratory, as well as from my wonderful mousey friends online. I also love learning from my terrific questioners here on AllExperts - you folks keep my passion for these amazing animals alive and well!

East Coast Mouse Association - expired, American Fancy Rat and Mouse Association - expired

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