I took my dog to the dog park today and as she romped around and jumped on the doggy obstacles and such I noticed that she had a bare (hairless) patch on her right hock. I immediately came home and I took a look at it. It causes her no pain whatsoever, doesn't look infected, but nevertheless, it...

My puppy has a weird path on her back. The patch has lost all the hair. The patch is blueish. I haven't noticed my puppy scratching the spot and it looks like it doesn't even bother her. Any ideas what this is before I go to the vet this weekend. Thanks,