My mare has been on and off again lame for over 5 months now. She is nine this year and for the three years previous she was never off a day and was worked hard. It was sudden onset three legged lame and varies between that and sound. It presented suddenly and she was literally gaiting (she is not gaited or of a gaited breed). I have had three vets look at her and a handful of farriers. There is no swelling or tenderness anywhere in her leg or shoulder and never has been. She has had x-rays and radiographs and her navicular bone shows no sign of decay or weakness.All vets say there are No navicular changes even though she presents every other sign that would lead one to assume it was that type of problem. Pain has nerve blocked to her foot right front foot, she has a raised digital pulse and comes up positive on hoof testers on the outside of her right front. She will seem sound under western, but as soon as she has a rider on english she goes three legged lame again. The last vet says all he can find wrong is that her foot was not balanced right but it was not that bad. A new farrier worked on her about a week ago. She was much sounder as soon as the old shoe came off and walked out sound. She has been much better but is still gimpy, now seeming to be stiff on either front foot, but not both at the same time. it seems to alternate. Any ideas on if there is some other underlying problem, or thoughts on this?