I just noticed that a deer (I’m assuming it was a deer since nothing fell) took a good chunk out of one my apple trees last night. Here is a picture of the damage. Is there anything I can do to seal up the damage before the rain comes later this week? Should I spray the wound to prevent fire blight from setting in? I’m planning to splash all of my trees w/ plantskydd (the first batch must have washed off) tonight but that doesn’t fix the damage incurred. 
Mickster, I would not think that pic shows deer damage, at least not for this time of the year.
For me, the deer are interested in eating young shoots and leaves while there are green leaves on the trees. In the fall, the males will rub their antlers on a tree stripping the bark, but even that typically leaves rougher edges, much like coarse sandpaper. Others can chime in, but it seems unlikely to be deer, IMO; I’d be looking for another culprit. If anything, it looks similar to the damage one would see if a metal edge of some implement hit the trunk, like a wagon or blade on a tractor going by.
As for repair, I would trim the loose bark off, putting a clean edge on it so that water won’t collect. You don’t want to pull any more bark loose, just cut away the stuff that is already loose. And that should do it. There has been quite a bit of talk here about pruning paints not really being necessary anymore.
I have to agree this doesn’t look like deer. I have had plenty of deer in my orchard and never anything like that. Weed eater, mower, unless there was a branch there and the deer ripped it off I’ve never seen this. Would agree with Steve top leaves normally get munched on. Not seeing any teeth marks like a large rodent. Not sure if that is the trunk or a limb but doesn’t look like deer damage. I agree with Steve on the repair… I lean a bit toward some sort of cover be it a sealant or something else.
Seen that sort of thing way too often when I’m mowing and I hit 'em with the tractor tire, or the mower swings over and knocks into them. That is not deer damage, IMO.
I have an ancient roll of 18-inch wide Parafilm that I got when we were cleaning out a storage closet some years ago… on those all-too-often occasions when I knock a big chunk of bark off like that, I’ll try to replace as much bark as I can find, wrap with parafilm and then cover with aluminum foil. Sometimes the bark seats back down and everything is fine… sometimes it has to heal in from the edges… but they will heal.
I remember my wife backing a trailer into one of my bur oaks in the yard - knocked off a chunk of bark easily 10 inches in diameter. I covered it, as above… had to heal in from the edges, but it only took it a couple of years. You could hardly pick that spot out now.
If it’s not deer damage I have no idea what caused it. I haven’t mowed in weeks and no truck could get to the location the tree is planted. If it was a falling limb I would have expected to see it dangling there. I’ll take your advice and remove any loose or torn bark and let the tree recover on its own.