A horse boot comprises a shell with front and lateral sidewalls. The sole has a longitudinal slot and an open rear end for access to the slot. The slot may be open or closed. A heel support includes a bottom plate for slidable engagement with the slot at a desired length position. Straps wrap around the hoof and connect the heel support to the shell of the boot. The heel support comprises a back plate and a heel cradle slidably coupled to the back plate for vertical adjustment. Straps extend forward attached to the front portion of the shell. In another embodiment a heel cradle structure includes bands fastened to the rear of the shell, thereby defining bulb retaining openings. A strap wrapped around the hoof is attached to the bands. The boot is fitted adjusting length and height to optimize the way it is fastened to the hoof.
