What is the theme in Chucaro: Wild Pony of the Pampa by Francis Kalnay?

Loyalty is a theme in the story. Chúcaro remains relatively quiet about the unusual relationship between Juan and Pedro. The Vaquero is Pedro's father, but Juan is his caretaker. Presumably, this is because the Vaquero is both elderly and an alcoholic who is unable to care for Pedro. Nonetheless, Juan does everything he can for Pedro. Explicitly depicted in the book is Juan's effort to help Pedro raise Chúcaro and train him and later protecting Chúcaro from being taken away by Armando and the mayordomo. Juan is one of the exemplars of loyalty in the book for this reason since he puts his job on the line to help Pedro keep Chúcaro. In fact, he ultimately lost his entire livelihood for Pedro's sake.