cobgoblin
Bugrit! Millennium hand and shrimp.
There is no one on here that has given me an experience of their horse having wee in its blood its all been speculation. Yes there are lots of reasons. Kidney stones. Bladder cancer. Urine infection. Kidney infection.
I can't see how someone else's experience would help you really as it might be due to a different cause.
Perhaps one fact you can assume is that this is not a particularly common symptom that others have had to deal with.