Any thoughts on beeeding a mare with a cyst on her navicular bone.  She is probably considered pasture sound and is very fat right now which doesn't seem to add to her unsoundness. I have held off breeding her because of it but I know people that are breeding mares far worse than her.  Vet said he just couldn't give me a prognosis either way.

Personally I wouldn't breed a mare with navicular issues due to the hereditary aspect, but I'm not sure that's what you were asking. Your vet can't guarantee your mare will be fine, so it's understandable they declined to give a prognosis to ensure you won't come back and sue them if something goes wrong.