That sounds reasonable to me too, but scary too. What have I done to my horse

? I have my horse done every 6 weeks, that means his back feet haven't been touched in twelve weeks. I am very worried about his frogs also. This same farrier told me something was wrong with my horses knees and he needed to be done every six weeks instead of 8 to insure that he stays sound. Do you guys see anything with his knees?