(barking) [onscreen text] Greater Swiss Mountain Dog. [male narrator] On a small farm in rural Missouri, breakfast is being served. Brigitte Rhinehart is feeding her farmhands. [Brigitte] Everybody, get! [onscreen action] Brigitte is placing bowls of food in front of her dogs. [Narrator] What they lack in discipline, they more than make up for in enthusiasm. [onscreen action] Dogs begin eating. [narrator] These Greater Swiss Mountain Dogs, or Swissies, will each go through about six cups of dog food a day, which is not unusual for an animal that weighs between 125 to 135 pounds. What may seem unusual for a dog this size is they don't drool. They have undeveloped flews, which is the loose part of the dog's upper lip that hangs down. This anatomical feature make Swissies a dry-mouth breed. So, while they may eat a lot, at least they're polite about it. Any farmer will tell you, it's important to have a good breakfast before a day of hard work. [onscreen action] A wagon is being loaded with wood. [narrator] And these dogs have been working hard for centuries. [onscreen action] A dog begins pulling a wagon load of wood. [Brigitte] Okay, all right, come here, Bo, come here, Bo. Good boy, good boy! [narrator] The Greater Swiss Mountain Dog was once the traditional working dog for Swiss farmers. It's strength, ability, and endurance led it to become respectfully known as the poor man's horse. [onscreen action] The dog is being unhooked from the wagon. [Brigitte] We should also keep in mind that this is a working dog and it has a somewhat maybe sharper edge than let's say a lab or a golden retriever, or some of the other very popular dogs. [onscreen action] Brigitte is walking through a cow pasture with her dog. [narrator] One basic difference is the way a Swissie typically greets a stranger. [onscreen action] Brigitte sitting with her dog. [Brigitte] A Swissie will not come up to you and wag it's tail without barking. One of the trademarks is actually they run up to you and stand just about three feet in front of you and just bark at you. [onscreen action] Man petting a dog. [Brigitte] They are of course, a very good deterrent in view of their size and their very impressive bark. [onscreen action] Dog barking. Dog walking around with owners. [narrator] At once obsessive and pleasant, their character is the result of centuries of breeding, a function of both tradition and utility. In the past, their duties went beyond pulling and carrying. They were watchdogs. So, they are cautious with strangers. They were companions as well as workers. So they have a sense of loyalty and affection for family and friends. [onscreen action] Dogs lying next to kids. [narrator] And they typically watched over children. So they're patient and gentle. [onscreen action] Dog pulling wagon load of wood. Dogs running around. Dogs playing. [narrator] These great dogs helped sustain farmers who couldn't afford horses or mules, drafters and drovers, soldiers, sentries, and friends. Rescued from the brink of extinction, a near-perfect blend of muscle, instinct, and devotion. [onscreen action] Girl hugging dog.