What is the main conflict in The Crossing by Cormac McCarthy?

Billy Parham and his younger brother Boyd are teenagers in Cloverdale, Arizona, in the early 1940s when a wolf, apparently having traveled up from Mexico, finds her way onto the Parham land and takes down several cows. Billy and his father, Will, begin to work a trap line, hoping to catch the wolf before losing any more cows to the wolf'shunger.