The truck runs four circuits a week, each one a fixed order of yards. A horse's slot is a position in that order, not a calendar date - so the visit lands on roughly the same weekday every six to eight weeks, and the yard always knows which morning to expect the truck.
The forge, anvil and stand travel on the truck, so hot shoeing happens at the yard, not back at a shop. Nothing about the work depends on a horse being trailered anywhere.
New horses are added between existing stops on a circuit, never ahead of a standing slot. A full circuit sometimes means a short wait to join - ask when you call, and the honest answer is given up front.
