Hi this could be due to a fungal infection maybe or even as daft as this might sound a moth...we have been known to find that a moth will attack the coats of mice...rare but not unheard of...a great shampoo for fugal infections & any skin condition is Sporal-D which you can buy online if your local pet store doesn't stock it but it is a very valuable item to have...either use some neat on a cotton bud & apply to the areas or bath them in it...cotton buds are the easy option for these sort of problems...the Sporal-D is great for a number of skin complaints & can even be used on humans...
I hope this helps you if getting your mice back to full fitness with a coat to match.Regards Jake
I hope this helps you if getting your mice back to full fitness with a coat to match.Regards Jake