I have gone through some poor experiences with vets who could have cured things but failed to diagnose properly or act quickly. What I would suggest is getting your collie referred to the nearest Veterinary College if your vet is at all slow or lacking in proactive attitude. On the plus side, I know of several cats and dogs that have survived cancer surgery and have been fine and dandy for many years after. Animal treatment, like human treatment has progressed lots in recent years.
If you need to refer to a veterinary school, your vet should be able to do that for you, though some are very reluctant as they see it as loosing money for themselves.
Re the effectiveness of going to a Vet School - my cat was booked in to be put down at the local vets as they said its illness was untreatable long term and he would die soon. My cat was lying about, no interest in life, clearly distressed, loosing huge amounts of weight. We found out about Langford Veterinary Small Animal Hospital, a part of Bristol University by ourselves - not suggested by our vet.
We were very lucky, our vet agreed to phone them and refer us. Our cat was with the hospital by the same afternoon of the first enquiry.
They had him for a about 4 or 5 days days and diagnosed pododematitis combined with a stomach problem and when we picked him up, you could not tell he was even ill - only 1 week from when he would have been killed. He was still thin, but jumping up on things and trotting about.
He is still on medication every day and would get very sick without it, but there is hope he will recover fully long term as he has a health issue that does resolve but takes ages. Ironically it is not all that rare in cats and although the local vets knew about it, they did not bother to investigate recent treatments for it.
Over 1 year on from nearly being killed he is still happy and normal in himself, no longer in pain, no longer slowly starving to death and to all intents and purposes seems normal in every way when observed.
Since then we have referred to Langford for a couple of issues for another cat. While we were last there, they were operating on a dog who had a tumour on the brain and they were accessing it through the roof of the dogs mouth. Last I heard they fixed the dog and it was doing fine.
If your vet is not doing well, refer to the veterinary schools as soon as you can. Its expensive if you have to pay for it yourself and dont have insurance, but ours gave a quote before any investigations were done so we knew what choices we had.