Sheep dog (6)
I believe the answer is:
collie
'sheep dog' is the definition.
(I know that Collie is a type of sheep dog)
This is all the clue.
(Other definitions for collie that I've seen before include "Silky-coated sheepdog" , "Popular kind of sheepdog" , "Long-haired sheepdog" , "See 2" , "Working animal" .)