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Ageing In Mice


Up to One Week: Mice are generally funny little wriggly pink things at this stage! They have their eyes shut and are pretty helpless – feeding and wriggling to be warmest at the bottom of the pile is about all they can manage. Even walking is more like waddling, if it is attempted. After three days or so pigment will start to show and the colour and markings of the mice can be seen. The colour and fur on the pups' tummies tends to develop slightly later than top colour and fur. The darker the colour the earlier it will show, as you can see below with this litter of self blacks. Light colours such as white, cream and dove will not show on the skin and will only become obvious when the fur starts to grow, as the skin in mice of these colours will be pink. The colour of a mouse's eyes can be seen from birth as their transparent eyelids allow black eyes to be seen through them, with pink eyes not showing up at all.

Left: self black litter at three days, Right: same litter at around five days

Week Two: The mice are a little better at wobbling around: their legs get stronger every day. They also start to get velvetty fur at around eight days. The difference in development in such a short time can be seen below. Pups are nice and chunky at this stage and will 'mob' the mother for milk almost constantly!

Left: pup before he develops fur, Right: same pup a few days later

Week Three: The eyes open at 14 days or so; after this mice tend to enter the flea stage, when they are very quick and jumpy. Make sure that mice at this age are in a safe place where they cannot jump/fall and hurt themselves. It is at this age that the pups start to develop more distinct personalities. The photo below was taken when the pup was 13 days old and had just opened his eyes.

This is the same pup as above (Eddie)

Week Four: By this time the litter is consuming solid food like nobody’s business, especially the bucks! Very soon they will be able to leave mum and become independent. At the age of four to five weeks, the sexes must be separated to avoid any pregnancies. The photo below is obviously a buck (!) which can become obvious when the testicles drop anytime from two and a half weeks onwards.

Eddie aged just under four weeks, before he was separated from his mum and sisters

Week Six: Babies can now be rehomed if necessary. They are independent but may still need a little socialising if shy. Most if not all will have stopped jumping by now and sit happily in your hands or climb up your arms to explore. They will be perfect miniature adults but should still be fed high fat foods for a while to help them finish growing to adult size.

Week Twelve: The babies will look very different to the small, wriggly pink ‘worms’ they started off as. At this age they are almost fully grown and does are capable of becoming mothers themselves.


Mice age in different ways, much as people do. Some will remain spry and agile and one day simply die of old age, while some will suffer illnesses beforehand, slow down and become more fragile.

Example(s) One: Humbug (17 months), Meka (16 months) and Niamh (16 months) at time of writing

Left: Humbug, Right: Meka

All three mice are active and very agile too. They have amazing strength and flexibility for a mouse of any age. All three are experts at climbing, whether it be rope, nets or toys (or me!). When they have reached the roof of their tank they then proceed to scale the wire mesh across the entire width of the tank – UPSIDE DOWN! One of my hamsters used to do a variation of this too – small animals seem to enjoy playing to keep themselves fit.

Climbing the roof - upside down!

When I first got Meka and Niamh (sisters from a pet shop, not fancies) they were quite shy. Now they are among the most dominant mice I have ever had, despite their small size. As soon as I put my hand into the tank they will come running to be picked up and just love being played with. They are also very trustworthy and I can happily leave them running around on my bed to explore while I sit in the room and read a book.

Humbug is also a great lover of people. She is perfectly content to snuggle up underneath my chin as I read or watch TV, and run up and down my arms and under my hair when I am on the phone. I had originally thought that she was infertile after trying to breed her from the age of four months onwards – but after several long periods of living with a pair of bucks (a father and son) she surprisingly conceived at the ripe old age of thirteen months, giving birth to and raising a healthy litter of girls (all the babies were does). She now lives with ten other does (including one of her daughters) who, despite all being younger, she has absolutely no trouble keeping up with (and showing up!).

Example Two: Whiskas (20 months)

Whiskas before she became ill

Whiskas was a different kettle of fish altogether. She was doing fine at a year old: no health problems at all. Then she developed a chatter that was more than just a cold and the vet diagnosed fluid on the lungs. After antibiotic treatments that she did not respond to, we had to accept that since it wasn’t harmful to her we would just have a funny chattering mouse.

Unfortunately after that her afflictions began to get more serious. At around 17 months or so she slowed down a little and developed glaucoma in one eye, which was inoperable due to the fluid on her lungs (the vet didn't feel she would survive the anaesthetic). A few months later she also got a large tumour between her neck and her front leg. When this got larger it began to impair her walking and made her waddle. She also seemed to slow down towards the end of her life in everyday things, and would sometimes breathe quite quickly. Having said this, she still had an iron grip and could easily complete vertical climbs on surfaces with little grip right up until the end.

When we eventually had to take her to the vet’s to have her put to sleep, the vet said that she thought Whiskas might have also had a tumour or tumours developing behind her (glaucoma) eye, just to complicate things. Overall, Whiskas coped very well with her ailments and went about a normal life – continuing to act as mother and grandmother (although she was neither) to all the other does she ever lived with.

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