Why do my horse's fly boots slide down, and how do I stop it?

Fly boots slide and gape at the bottom for two reasons: the boot is shaped like a straight tube while a horse's leg tapers (wider at the ankle, narrower below), and mesh soft enough to be comfortable has no structure to hold itself up. The fix is usually boots with built-in stays — flexible vertical inserts that keep the mesh cylinder standing — plus correct sizing and placement.

Fitting checklist: size by leg circumference, not just height; fasten snug enough that you can slide one finger under the closure (looser than that and the boot walks down within hours); position the bottom edge just above the fetlock rather than over it, so the wide ankle joint isn't pushing the boot open from inside; and re-check after the first hour of turnout, since new boots settle. Some horses simply wear one brand better than another — leg conformation varies as much as boot patterns do.

If a boot consistently gapes open at the bottom overnight or your horse steps on it, stop using it until you resize or switch styles — a trailing boot is a tendon injury waiting to happen. And if the skin under a boot is rubbed raw or swollen, give the leg a break and let your vet look before continuing.