More than likely it's just hard fighting. Might be some poor genetics but I'd doubt it. If you haven't seen it in the past, and don't see it again in the future, chalk it up to a tough year of fights. I doubt there are any minerals or such you could put out that the deer would eat enough of to really make a difference.
“There are two spiritual dangers in not owning a farm. One is the danger of supposing that breakfast comes from the grocery, and the other that heat comes from the furnace.”