Blood in the urine could come from: Uterus, cervix, vagina, urethra, bladder, ureter or kidney... It's impossible to tell from the symptom you have described. Has she been covered naturally? The most common reason is vaginal trauma, but it is very hard to say. If the mare's gums are VERY pale, or she seems distressed, she MUST be seen now. In any case, she should be seen by a vet as soon as possible.
It is coming from the bladder, definately not vaginal trauma. She is a bit 'dull' which is most unlike her but the vet says ok to wait until tomorrow to get her to vet here. Everything i read tends to give dire predictions - is there any chance it could be a simple infection easily cleared with ABs?
Are you certain it's not vaginal trauma? Look for one of these patterns:
Blood at the start of urination will be symptomatic of vaginal or uterine bleeding.
Blood througout urination is symptomatic of bleeding in the bladder.
Blood at the end of urination is symptomatic of bleeding from the ureter or kidney.
Which one is it? Or none of these?
ok, vet has done endoscopy, scan, blood and urine tests. The bladder looks like it is ulcerated so could be bladder infection but I think the blood which is still happening is a bit of a mystery. Anyway time will tell.