Large wounds like this especially on horses should be kept covered to prevent drying out. MOIST WOUND HEALING is the way to go. If the top scab forms over , an infection can stay underneath , lengthening the healing time. Horses heal from the inside - to the outside so we want the underlying area to fill in first. If we heal the top layer first in takes the new cells underneath longer to join up. Yes good ole copper sulp paste will help with the proud flesh or if you have the stomach for it, scrape it back with a scapel or razor blade but it will bleed profusely. As the days go by, lengthen the bandage change days as the less you fiddle with it the better.I need to take photos of my mare and post them, she did this 7 years ago now but far worse, she did front and back tendond and couldnt walk as the hoof would flop about, now she is totally sound and has a neat scar.