So this is more for advice on how to handle a friend.
I have a friend who euthanized her 14 year old horse about 3 months ago. Both of his parents had navicular, and passed it on to him. He was not even pasture sound. He was in a terrible amount of pain.
Said friend treated it for well over a year with different shoes, supplements, medicines (which gave him ulcers), x-rays, various vets and specialists.
Now she's off in farrier school and was showing the x-rays to a professional there, who is pretty sure that he would have been okay with additional treatments and changing the palmar angles and that he thought the navicular bone was actually okay.
....so now she's second guessing herself and she's not very sure she did the right thing.
If you were in this situation, what can you even offer to say? I'm really at a loss.