A photo-essay that shows the largest equine breeds— Percherons, Belgians, and Clydesdales—in actual working situations and as participants in an exhibition. Fascinating nuggets of draft-horse lore are embedded in the simple text: A century ago there were 27 million such horses at work in America; Percherons are descended from the huge medieval warhorses that carried armored knights; one horsepower is accessibly defined as the amount of force necessary to raise a weight of 150 pounds from a hole 220 feet deep in one minute (although that definition is buried in a note on the copyright page). The full-color photographs include close-ups of hooves, harnesses, and the strong, patient faces of both horses and owners, as well as working rigs of many types, from a plow hitched to a dozen Belgians, to a one-horse open sleigh. Particularly appealing are the pictures of foals and of young people feeding, shoeing, driving, and admiring these gentle giants. Workhorses have been overshadowed by their flashier cousins; it's good for young readers to be reminded of their beauty and historical importance. (Picture book/nonfiction. 5-9)