In Michigan, it’s legal to kill any dog running, chasing and/or killing deer. Period.
I suspect the deer around this poster's home are underfed and small which is why a border collie was able to take one down ~ as we move into winter it's only going to get worse, and there will be a major die-off from starvation as these deer overgraze their limited mast.
Better they die quickly at the hands of canines than by starvation.
That's nature's way.