Old Mouse Breathing Differently

Question
I have 2 female mice about a year and a bit old. In the last couple of months one of them (Smidge) has started squeaking seemingly when she breathes. It's usually a very small noise and isn't constant. It seems most prominent when she's sleeping. Sometimes when she isn't squeaking like this she makes a small sort of clicking noise when she breathes. She doesn't seem to be showing any other signs of illness, she's active and curious, eating and drinking and the other mouse isn't showing any symptons either. If I hold her up to my ear it seems like she might be wheezing. Is it likely to be asthma and if so what can I do to help her breathe more easily? If it's not asthma do you know what it might be?
Thanks for your help
Jo

Answer
Dear Jo,

Your mice have reached quite a venerable age.  It would not be surprising if they began to develop symptoms of age.  The breathing may simply be a result of age.  The other cause for breathing sounds is if the mouse has- unbeknownst to you- had a respiratory infection.  This can change a mouse's breathing for good.  It isn't a bad thing and it won't affect her health.

Mice can live up to 3 years, so they might still have a long way to go.  

squeaks n giggles,

Natasha