I am Trying to find a pretty old book, was wondering if anyone would know of it?

the book has a cover that depicts a snowy area with silver birch trees and a running fox or little dog? I read it when I was 11 or 12 and have been searching for it since a few years ago? I can't remember much about the main plot, but I think it was about a female fox or a small dog that was trying to mother and protect her pups/kits in mid winter? There might have been humans involved but I honestly can't remember, though i do know it was a good book. I know that's not much to go on but does anyone know of such a book?