QUESTION: Ok, so I'm back. And I have some young mice I bought that are all pretty healthy; except there's ine mouse which baffles me. I've asked everyone I know who knows anything about mice(or rats) and they've all said she was just the runt of the litter. Are they right? She is smaller than the others, but she isn't showing any signs of ailment(yet) at least none I know of. She typically is the outcast, though; but they don't really bully her out of food. Actually, just the opposite. She will shove the other mice away sometimes, but doesn't really fight with them. They have a network of tunnels they have created, and my "runt" seems to always be at the entrances to the tunnels, slowly munching or cleaning. Also, she is either very tame or starting to get ill, although there is another mouse with the same behavior when handled. Whenever I pick them up, they act normal for the most part, but while the other mice flinch away from my touch, especially then touching their bellies, those two don't. Is that normal? Also my "runt" seems to be out a lot, but is almost always by herself. I'm concerned though.  Mostly because she has rather slow, precarious, ironically cat-like movements. Like she's always walking over broken glass or dead things. She also seems to be photosennsitive(she squints a lot)which I would expect from a sick or even albino mouse. However, she's blue-black, not albino.her eyes are a normal dark color. Sorry for the long-ass email, but I have virtually no experience with mice, as you can tell. But hey, you can't gain experience without trying, and no pet store I've seen has a manual for mice, and the internet tells you so many different things its easy to get confused. And please do not recogmend a specialty vet. I can't afford one and the nearest one to me is about 126mi away. Thanks!


What you are describing is very characteristic of runts, but I cannot tell from here if there is anything else going on.  Frequently, a runt of a litter is the last mouse out of the uterus, and can be the last one to get to a nipple.  This can result in fewer antibodies received from valuable colostrum milk, which sometimes leads to slightly weaker immune systems.  Runts typically catch up - it can just take them a little while!  Another cause of smaller mice is if they actually implant in the uterus later than their siblings, which means they are literally younger when they are born.  Again, she'll catch up, it just may take her a few weeks more.

It sounds like she has a great temperament (letting you pet her is a wonderful thing, as long as she does not seem stressed, and this is ruled both by genetics and by early handling), an excellent appetite, and a healthy energy level.  Her manner of walking is unusual, but I cannot say if she is having some physical difficulty with movement, or if she is just trying not to attract the attention of her stronger littermates.  The photosensitivity may just be a developmental thing, unless that is a recent problem.  As long as her eyes are clear, not bulging, responsive, and she is active, I would not suspect an illness.

The real test is if she has been behaving this way her whole life (moving slowly and catlike, calm responses to handling, and squinting in the light), in which case I would expect this is just her roll on the genetic dice.  Of course, if she is slow-moving now but used to be very hyper, then I would suspect that something is bothering her physically.  It boils down to what is her personal "norm," apart from her siblings.

You are right that it can be tough to find quality mouse information.  One resource that I found to be very useful when I was starting out (besides experience!) was mouse breeding forums.  Folks who breed for show all over the world tend to congregate online and share their wisdom and help each other out - there are also several great facebook groups you might consider.  This forum is full of great info:


Hopefully I helped out.  I don't think your little runt needs medical attention, but again, if you notice a change from her personal "norm" then I would start looking for potential stressors.  She just sounds like a sweetheart to me, though!

Best of luck, and let me know if I can help with anything else,

---------- FOLLOW-UP ----------

QUESTION: Ok, so I need an answer asap. My pregnant mouse just had her first pinkie of the litter, and. She killed it in. Cold blood. I know this can be expected from a first time mother, especially when said mother is sick with an upper repiratory infection and isn't responding to treatment; but will she kill them all? One or two I can understand, but what about the future ones? I have done my upmost not to mess with her, and I have spent a ton of money to get A mouse to hve a litter, seeing as how upper repiratory infections, altitude sickness, and gastrointestinal problems seem to be contagious in my house for both the mice and, to a point, me, which makes breeding difficult. That and my males seem to constantly either starve, or more often then not eat themselves to death, and usually die of intestinal issues medicine isn't working to fix. I clean them regularly, so...but please, I've worked very hard to get to this point on my own. I need an answer as soon as possible, just so I at least know what to expect. Thank you.


This doesn't sound like a healthy colony to me, and breeding unhealthy mice is a recipe for disaster and heartache.  For starters, there are no medications of which I am aware that are safe for a pregnant or nursing doe, meaning treating a pregnant mouse with a respiratory infection is just as dangerous and potentially lethal to the pups as letting a sick mouse give birth - neither is safe for mom or pups.  Although stress and mothering abilities both can contribute to canibalizing, more often than not a mom knows something is wrong and kills the pup intentionally.  This is the same logic as when she feels they may be in danger - it is better to conserve the energy than to raise a litter that will not survive.  If she is ill, the pups may not have been viable, or they may have been ill as well.  She would know this long before we could.

I cannot predict for you how the rest of her litter will turn out.  You may wish to try bottle feeding them, especially if she is on antibiotics, but this can be extremely difficult with pups that young.

Please be patient, and wait for your colony to stabilize.  Healthy, happy mice will breed healthy and happy babies.  Is there another breeder in your area who can give you healthier bucks?  Also, respiratory infections are extremely contagious - it is best to give all recovering mice three weeks without symptoms before adding cagemates, breeding, or bringing in new mice to even the same room.  Be careful to sanitize all tools or anything that goes between cages, and be careful going between cages when changing them.  Treat all mice exposed (except for pregnant/nursing) when giving medications.  You probably already know all of this, but respiratory infections can wipe out whole colonies, and every breeder encounters one sooner or later.  It will be well worth your patience - as losing a litter is just as frustrating, for sure!

I am sorry for your difficulties and for the lost pup.  Remember to be there for the momma - this is just as hard on her as it is on you.



All Answers

Answers by Expert:

Ask Experts




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: http://www.rmca.org/Articles/orphans.htm Orphaned Mice Videos: http://www.youtube.com/user/CreekValleyCritters/videos?query=raising Natasha's Your First Mouse: http://www.youtube.com/watch?v=RNK4uqNZTbA&feature=share General Mouse Help: http://www.fancymice.info/ Mouse Info and Exotic Breeds: http://www.hiiret.fi/eng/species/


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

Partial University for a B.S. in Microbiology, Partial University for a 2-year degree in Veterinary Technology (RVT cert), C.E. classes in pathogens, aseptic technique, genetics, and applications

©2017 About.com. All rights reserved.