Adaptation Expansion: In the book, Travis puts Old Yeller out of his misery immediately after learning he's got "hydrophoby", all of it happening in less than a full page. In the screenplay, Travis is unwilling to believe that Yeller is that sick and instead decides to pen him up for a few days and see how he does, making it all the more heartbreaking when he's forced to accept that his best friend can't be saved.
Career Resurrection: Robert Stevenson had a decent directing career in his native Britain in The '30s when he was invited by producer David O. Selznick to come work in America, but most of the projects he made across the pond were unsuccessful. His career had been languishing for nearly two decades when he was given this project by Walt Disney, with its immense success putting him back on the map and leading him to have a successful run working at Disney for the rest of his life.
What Could Have Been: The scriptwriters wanted to put in scenes of the cattle drive that the father leaves the homestead for, as they didn't want the film's biggest name to only appear the beginning and end. Walt Disney vetoed this idea, eliminating over 35 pages of script, saying "We bought this book because we liked it. Why change it?"
