He hasn't been on pine since we first noticed it. It's still dark red on shredded paper. Once it dries it turns slightly lighter and browner, but not necessarily as extreme as the color change of dried blood.
Thanks, I feel a lot better now. I have seen a pretty wide spectrum of rabbit urine before, but the dark blood red/brown freaked me out a bit. At the same time, if it WAS blood, the little thing would be dead by now for sure. I will try a little vinegar as you suggested, and let him have some...
I work at an animal shelter, and we got two rabbits in almost exactly a month ago, a male and a female from the same house (separate cages). They were kept on carefresh, and were switched to pine. Shortly after arriving, the male sprayed VERY red urine ALL over the cage, walls, counter...