Shetland sheep dog vs sheep dog

Shetland sheep dog and sheep dog both are nouns.

Word	Noun	Adjective	Verb	Adverb
Shetland sheep dog	Yes	No	No	No
sheep dog	Yes	No	No	No

As nouns, sheep dog is a hypernym of Shetland sheep dog; that is, sheep dog is a word with a broader meaning than Shetland sheep dog:

Shetland sheep dog: a small sheepdog resembling a collie that was developed in the Shetland Islands
sheep dog: any of various usually long-haired breeds of dog reared to herd and guard sheep

Other hypernyms of Shetland sheep dog include sheepdog, shepherd dog.

Shetland sheep dog (noun)	sheep dog (noun)
a small sheepdog resembling a collie that was developed in the Shetland Islands	any of various usually long-haired breeds of dog reared to herd and guard sheep