Details
Horse armor does not have durability and can be found in dungeons as well as randomly generated chests in the Nether fortresses, in Desert Temple chests and in abandoned mineshaft (minecart) chests.
Horse armor is an item, a special type of armor that can be given to a horse to wear.
Placing armor on a horse will cause any previous armor to be removed and drop as an item.
Minecraft Game:Horse Update 1.6.2