Shep is the informal short form of Shepherd — which functions both as a surname, an occupational name, and a direct descriptor of the German Shepherd breed. For a male dog, it's a name with a long Western pastoral tradition: Shep is what you call a working dog in a language where names didn't need to be elaborate to carry meaning.
The Shepherd Tradition
Shep appears in American folk music, cowboy culture, and the rural naming tradition as the archetypal loyal dog name — the dog who waits at the train station, the dog who finds the lost child, the dog who stays. The most famous Shep in American history is the Montana sheepdog who waited at the Fort Benton train station for five and a half years after his owner's body was shipped east for burial, becoming a national symbol of canine loyalty. The human name Shepherd has grown among parents who love the occupational-name aesthetic.
Breed and Working-Dog Fit
German Shepherds are the obvious Shep breed — the name describes the dog's heritage directly. But Border Collies, Australian Shepherds, and other herding breeds carry it with equal logic. For any working-dog household, Shep reads as honest and appropriate.
The Counter-Reading: A Very Pastoral Register
Shep on a Pomeranian or a Shih Tzu creates a gentle genre mismatch — a toy-breed dog in a working-dog name. That dissonance can be charming or slightly incongruous. The name works best when the dog has at least some claim to the pastoral tradition it invokes.