I was a farrier/horseshoer in California back in the late 50's and through the 60's. We called the aluminum shoes "racing plates" in those days. In fact your aluminum shoe looks just like what we called "racing plates." They were used at the race track on thoroughbreds and quarter horses at that time. From the one page that has been posted, apparently aluminum shoes are more common now, but shoes of the type you have posted were only used at the race tracks in my day. The shoers at the track were unionized and got paid big bucks for plating the race horses. The horses had to have new shoes for each race. I was getting $8.00 to shoe a horse, and the rumor was the closed union shoers at the track were getting something like $60 per horse. One account I had was trimming the feet of quarter horse brood mares, but anything that was going to the track I didn't get to touch, because the lock that the union shoers had on work done on horses feet at the track.