@Arizona Docent Maybe, as there was mention of Heck's Cattle on the informational sign. The two horses in this photo look slightly different from most horses that I've seen in zoos or on farms.
The first two links will explain the thinking behind the Heck horse and how it was created.
The other three links will lay out how Heck Horses came to be in the USA, their history in this country and how Shalom Wildlife Sanctuary got it's herd.