# At what temperature will mice die of heat exhaustion?



## Frizzle

One of the local breeders in my area lost most of her stock due to her air conditioning breaking & her mice dieing of heat exhaustion. Being located in the same area, I would like to know at which temperature it becomes stressful for my mice, and how long exposure to that temperature becomes deadly. They are currently living in the upstairs with me, where it has gotten to the upper 70s low 80s so far, and I'm thinking I will probably move them down into the basement for summer. At what temperature range in the fall will it become safe to bring them upstairs again?


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## ThatCertainGlow

As far as I recall and have experienced, it's not the temperature, so much as a sharp change in temperature, towards the hot range, that causes the problem. If they slowly get used to the normal day's temperature from February until July (such as in a house in FL, without central AC) they are fine. Especially if you have some form of dehumidifier in humid locations. Mostly people who breed mice outdoors in hot areas just note that they breed less in the summer, or the litters don't thrive. I didn't experience either problem, but it wasn't exactly outdoors either, and I know I had less stocking density then the people I've read about online.

Outranging days, like 95 -100's, it's best to supply them with frozen peas, frozen mason jars of water, frozen mealworms would be good, etc. No plastic houses in such conditions. Those can be dangerous as well as stuffy, in my opinion. Wood is fine. Hay is better. I also offered them bathes on extra hot days. Which they all took, some with wild glee.

This was in a sloping tub, so they had a range of 'beach' (a folded dry towel they'd hop up on), wading pool, and full emersion. Most places are worried about mice being wet, and then getting a chill. If you can fry an egg on your car with minimal effort, my guess is that danger is slim. Just mentioning that because everything will say how dangerous getting a mouse wet is. I didn't experience this.

You really don't want them too adapted to the heat though. Mice bred in colder conditions reportedly grow larger, with better fur density. Just like any mammal, but more noticeable in one person's lifetime, with mice, because their generations are so fast. Siamese and the like are better when colder bred, as well, from what I've read (no personal experience). Obviously it's not in most fanciers interest to get breeder mice accustomed to heat, for any long term.


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## sys15

i kept my mice in a garage last summer, without any fatalities that i could attribute to heat. outdoor temperatures occasionally reached over 110 f, and i'm sure air temps at chest height within the garage was at least that at times. the mice's cages were in contact with the cement floor, which stayed considerably cooler. at high temps i would usually see that they had cleared a space of bedding and were lying on the bare plastic.

they bred throughout the summer. i didn't keep close enough tabs to say if they exhibited some decline in fecundity compared to during cooler weather.


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## ThatCertainGlow

sys15, have you noticed any type/size or fur changes, or was the garage a one time thing? I keep thinking back, but I can't recall ever noting (in the 6 or so years of breeding) a fight against decline in type, size, or fur density. Obviously I wasn't breeding for very long, perhaps not long enough for there to be a noticeable change. You'd think I would have noticed overall size declining in the blacks, at least, during that time frame, if it was going to happen, from constant heat.

North FL doesn't exactly have a fall/winter of note, nor much of a spring season. It's often uncomfortable by March. Muggy heat early in the mornings, Oppressive heat by 9 am. No moving air, most days, from April through September. Randomly has pleasant days from October through Dec, but it's still shorts wearing weather. Jan/Feb might be: comfortable, moderately cool enough to pretend a sweater wouldn't be too hot, or just wet, and bone chilly. South FL is better, because of moving air during the hot months. (Background on the temps. in that location.)

Wasn't breeding for a pointed mouse, though. Just ae blacks, and e/e yellows. Didn't have room for anything else, although a few siamese popped up in the blacks. All those changes are reported in natural settings, with wild mice. Not sure it even applies to well-fed mice in captivity. There is some blurbs, in places, about English show winners coming more from those mice being raised in outdoor sheds vs indoors. Not sure what that's based on, or the accuracy of such statements. Might have zip to do with temperatures, either way.

An add to the other things that reduce heat stress, and sys15's concrete floors made me think of it. Marble tiles/slabs/etc under the cages, are pleasant. Nice to walk on in such heat as well, for the same reasons. Just like concrete floors are cooler, marble is even nicer. These can often be had as trim remnants from tile places. Had a good few of those, and my mice did just as described. Hollowed out the sleep spot to the bare glass tank bottom. I got mine free, from someone replacing their floor. (The marble was discolored, or something.)

A whole house window fan is amazing. (Make sure to open opposing lower windows, interior doors, and such, or you will break it.) I would use one here, from morning to about 10-11 am, if we didn't have two sections of delightful AC for both floors of the house; and 5 cats who are not allowed in any room with mice. Those things would also double as an exhaust fan too. Might be good with buck odor, if someone objects to it.

If I lived in a place where basements were reasonable to have, I would keep the mice there, provided they wouldn't be in the way. It's definitely not necessary though, especially if summer is only a season where you are; unless you acquire mice who are not yet adjusted to warmer temperature ranges.


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## Laigaie

As they said, sudden changes are your biggest problem, but prolonged temps over 85 have had serious negative results in my mousery. Prolonged temps over 80 mean I get reduced fertility and increased infant mortality, and the longhairs and pet-types start having trouble at 80. The larger and more robust mice have problems over 85, however. Mostly, the heat kills the weak. Small mice, sick mice, old mice, all go first.


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## sys15

ThatCertainGlow said:


> sys15, have you noticed any type/size or fur changes, or was the garage a one time thing? I keep thinking back, but I can't recall ever noting (in the 6 or so years of breeding) a fight against decline in type, size, or fur density. Obviously I wasn't breeding for very long, perhaps not long enough for there to be a noticeable change. You'd think I would have noticed overall size declining in the blacks, at least, during that time frame, if it was going to happen, from constant heat.


my mice are still in a garage, but we moved, so it is a different garage. this one is more shaded and seems to stay a little cooler. we haven't hit the really hot part of the year yet though.

i didn't notice any change in type/size or fur, however the extreme temperatures are really only for july and august. june and september are hot, but not that hot. it also usually cools down pretty well at night, so the extreme high temps are not throughout the entire day. and the same colony is subject to cool temps during the winters.


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## Frizzle

Thank you all for the advice! Does anyone know what range the temperature fluctuation needs to be?


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## ThatCertainGlow

My current upstairs mice (pet-type) act like they don't care for anything around 80 F. They are not damp or anything, but they don't look content. What I've read is that mice accustomed to the 70-75 F range are not at all happy at 85 F, and it gets dangerous for them after 86-90 F. I've not exposed mine to much above 80 F, due to the AC usually works, and it was set at 72 F. Sometimes it has overloaded this year, during high ninety days and cuts off, letting the temps climb to low 80's F. I've changed it to 74 F, so the ends of the room are max around 76-77 F, but at least it doesn't cut off.

Not sure how hot it would be in the days that reach over 100 F outside, haven't hit those quite yet. I can't remember what temp range change has killed mice, en-mass, of breeders on this forum. If I recall it was usually an artificial temp that was being maintained, and then the sudden loss, or artificial increase due to malfunction, is what killed, and mostly the weak; as Laigaie mentioned above.

However... she said this happened to the weak ones, for her, in the summer, and I don't think she uses AC, so I suppose a killing range/change depends? At least for the young, old, infirm, etc. I didn't have the little pet-type in FL at those previously mentioned FL temps. Didn't know they would have a different heat tolerance, and will now keep that in mind.

I bred (and breed), long haired/angora. They often seemed to be the canaries, and yes, they warned me, first of all the mice, that it was time to break out the cooling materials, if I wasn't already aware. Those were the larger robust versions of mice though, and didn't seem to have trouble until around 90 F.

The new, more standard/typier mice haven't been exposed to much temp changes, but their AC works better at holding temp steady. (Still in QT.) So no info on ranges yet. (Hope I won't actually get that info... go go go AC...)


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## Laigaie

In the old house, I had AC but not in the mouse room. It was cooled by having the door open to the rest of the house, and was routinely 80 in the summer. If someone closed the door, or the outside temp went crazy high (115 is not uncommon in late July), I'd start losing angoras, retirees, and litters. That was when it would go above 85. At the new house, we have no central AC at all (only a window unit on the entire opposite end of the house), and it is already hitting 78-80 in the mouse room at the hottest part of the day, down to 68-70 at night. That's a full 10 degrees less than outside at the hottest part of the day, but when it hits 115 outside, I'm going to be totally done for if we don't get more effective AC in this house. I'm hoping that the gradual acclimatization will help reduce heat-related issues this year, and I'm trying to get my summer breeding in before it gets too hot.


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## sys15

the high supposedly hit 104 here today. i had a thermometer on the floor of my garage (the element not touching the floor, maybe .25 cm above it) and it read 96 in the late afternoon.

supposed to get be around 110 for the next five days. perhaps worse, it's only forecast to get down to about 80 nights. kinda scary.


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## YuukikoOgawa

From what I've heard, ventilation tends to be the bigger factor, so the ideal temperature range depends somewhat on what kind of housing you use.

I've got a 10-gallon plexiglass tank with a mesh screen top for my mice, so I'm a bit more careful about monitoring the internal temperature because the limited ventilation (through the top only) and the clear sides mean the temperature inside the tank might be a lot higher than the rest of the room. Thankfully, plexiglass is nowhere near as bad as glass when it comes to trapping heat!

You can get a little round thermometer from Petco that you can stick to the inside of the cage, just out of reach of the mice, and that might make it easier to keep track and see exactly what temps your mice seem to become uncomfortable.

Another method for cooling off that I've been using, during occasional extra hot days, is cheap ceramic tiles that I stick in either the freezer or fridge. I put one chilled tile in one corner of the cage, so that the mice themselves can decide if they want to lay on the cool time or stay in the warm hide. They're about $0.13 each at the local Home Depot, and at the very least the mice seem to like licking the condensation off.

The key thing, I think, with cooling off measures is giving the mice options and letting them decide what they want for themselves.


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