Smoky

Smoky the Cowhorse is a novel by Will James that won the 1927 Newbery Medal.
The story details a horse's life in the western United States from his birth to his eventual decline. It takes place after 1910, during which the West dies away, and automobiles are introduced. Smoky is born in the wild but is captured and trained by a cowboy named Clint. Smoky's intelligence and spirit take Clint, and he uses him as his personal steed. Under his guidance, Smoky soon becomes known as the best cow horse around. However, Smoky is among several horses stolen by a horse thief. When Smoky refuses to allow the thief to ride him, being loyal only to Clint, he is beaten repeatedly in punishment.
Developing an intense hatred for humans from this treatment, Smoky eventually attacks and kills the thief. When Local authorities eventually capture smoky, his now violent and aggressive demeanor prompts his use as a bucking bronco at a rodeo. Under the moniker of "The Cougar," he becomes the most famous rodeo attraction in the South West, and people come from miles away to attempt to ride him. But, unfortunately, years of performing at the rodeo eventually take their toll on his body and spirit, and he has left a shell of his former self. As he is no longer of any use as a rodeo horse, he is renamed "Cloudy" and used as a riding horse, then later sold to an abusive man who starves him.
During this time, Clint finally reunites with Smoky. While in town on business, Clint spots and recognizes the horse. After having Smoky's current owner arrested for his acts of cruelty, Clint reclaims him and takes him home with him. Although Clint initially despairs at the condition Smoky is in, his careful treatment of the horse begins to show results. In the end, Smoky has completely recovered his former health and personality.