Okay, I came home late tonight from work, sat down, and picked up my dogs brush. I haven't groomed him in almost a month, as I've been insanely busy, but tonight I was gonna give him a good brushing. He's a 13 year old black Chow Chow and weighs about 50 pounds. The first thing I noticed was that his rectum seemed to be red and swollen, maybe even bleeding, and there was feces stuck to the hair around it. (not typical) Then I saw a large spot where his hair was thinned out, maybe 6 inches across, on his left side, stretching from his anus, to his testicles, and around the left side of his hip onto his leg. Touching it made him yelp, and try to bite at me. He's in a large fenced in yard, so he's not been bitten by another dog. I'm kinda panicked, considering I've spent the last 4 hours searching for what this could be on google and didn't find anything that exactly fit. I'm trying not to panic and plan to take him in to the vet first thing in the morning, to see what's going on. Or should I be more worried, and take him to the ERVet right now.