If a horse can get their foot around it they can get a laceration. I have seen a number of these over the years from mild to major. Caused by wire, metal siding, fencing, a horse over-reaching on itself. Some of the mild ones you can get away with bandaging until completely healed, others will require stitches and bandaging, and others will require hospital stays to clean the wounds daily to every other day and then will be sutured and a cast put on so it will heal properly. The general rule of thumb for any leg injury is to have a vet look at it immediately, since there is not alot of muscle and tissue covering the leg, even what looks like a minor cut could turn out to be a major problem if it is not treated properly. With leg injuries it is better to be safe than sorry.