Kray Gelder (and Baspinal) are correct, it is horse-shoe. But its more specific ID is, a "corrective" horseshow, used on a damaged or deformed hoof. See the pho below. Insofar as I'm aware, the version you found does not go back past the late-1800s. I've never seen a reference to that version being in existence at the time of the civil war.
But... I do NOT think I know everything there is to know about horseshoes. I invite anybody here who has specific knowledge for time-dating your version of "corrective" horseshoe to speak up.