What does an unhealthy mouse look like?

You can learn the most about your mice through their behaviour, appearance, and body language. It’s important to continually observe for abrupt or subtle changes happening with your mice. Because they are a prey species, they will try and hide signs of illness – so when they look sick, they’re really sick! Picking up subtle changes early can make a huge difference to your mice’s heath.

The first thing to do is to sit still, look, and listen. Waiting for a few minutes gives your mice a chance to stop pretending they’re healthy. They might be good at hiding signs of illness, but they can’t keep it up for long. The following are some things to look at and listen to once your pets have gotten used to your presence.

Behaviour

Check them morning and evening when they are normally active; observe the individual and group behaviour of the mice in their enclosure without disturbing them. Often the first sign of an unwell mouse is the mouse being isolated in the corner rather than nesting with enclosure mates.

Observe each individual mouse in the enclosure to see if they are moving, breathing well, sitting normally, and have bright eyes and a shiny coat. Watch your mice closely. Any changes in their feeding, drinking, social behaviour, or general activity may be an early sign of a problem.

Noise

Listen for any sneezing, especially if more than a few sneezes over an hour or two. This can indicate respiratory problems that require veterinary investigation. Mice aren’t as vocal as many animals (if they were, that would attract predators) so, while vocalisations don’t automatically mean there’s something wrong, unusual noises should be investigated. This includes crying out, squealing suddenly, wheezing, coughing, etc. For example, it could indicate pain if your mouse suddenly screeches, squeaks, whimpers, or makes any other sound that wasn’t made before when moving, interacting with their enclosure mates or you (e.g., being touched or picked up).

Appearance

Mice who are in pain or unwell often have a hunched posture with their back arched. A stressed or sick mouse will often have their ears pulled back flat against their head (compared to a happy, healthy mouse whose ears will normally be forward facing or reacting to what is happening around them) and they may have squinted eyes (a grimace) too. Changes in facial expression are a useful way of assessing pain in mice and a standardised scale (called a “Grimace scale”) to assess these is available (developed for use in laboratory mice but equally applicable to pet mice). You can find out more about the Mouse Grimace Scale here.

Mice are fastidiously clean animals – if they seem dirty, unkempt, their fur is matted, they have diarrhoea/faeces stuck to their coat under their tail, or there is discharge from their eyes, ears or nose, something is going on. Excessive scratching and general signs of itchiness are also abnormal.

Closely observe how your mice breathe. If you observe them frequently, you will know what is normal for them and be able to recognise when something isn’t right. Mice with respiratory issues will often breathe faster and with more effort than healthy mice; in particular, they may use a lot of effort in their abdomen to breathe, so you will see their abdomen moving a lot with their breathing effort.

Appetite

Mice love their food, and are constantly looking for, and eating it! If they seem less interested in food than normal or are refusing to eat, something is going on. This is never a symptom to ignore and could be caused by many different things.

Thirst

Increased water intake, along with increased urination, can be a symptom of a bladder infection, kidney issues, or other health issues. Take note of any other symptoms you’re witnessing and discuss them with your veterinarian.

Gait

Stumbling, weakened legs, limping, shuffling, and any other changes in how your mouse moves are all things to watch out for. They can indicate neurological problems, trauma, muscle weakness, etc. Favouring one leg could be due to something as simple as a torn toenail or as serious as a broken bone.

What’s next?

If you have detected an abnormality by looking and listening, it’s time to take a closer look. Physically examine your pets regularly by running your fingers gently over their body to check for any lumps, bumps and that they are physically normal. It is a good idea to get your mice used to be gently handled and examined from a young age using positive reinforcement and reward-based training. See this article for more information on interacting with and handling your mice.

If the issue you have detected is not something simple, you will need to take your mouse to a veterinarian experienced with mice, who can work with you to find out what is wrong and treat it appropriately.

Remember that anything that alters the smell of an individual mouse may cause social disturbances within your group of mice, including aggression. So, if you need to take one of your mice to the veterinarian, take the others too, or at least one of their enclosure-mates, so that they smell similar when they return.