
Hi,
Just my opinion, but in many breeds 8 would be fine - assuming from your name that this is a Dane, so a shorter life span than many breeds plus intolerance to anaesthetic - I would take your vet's advice on this, and have all proposed tests before going ahead.
That said, (from personal experience!) in general I would rather spay as a preventative when you know the bitch is fit and well - having had a 12 year old with a pyo, who then had to be spayed as an emergency, I would now aim to spay by approx. 8 in all cases.
M.