Dog some breeders had owned (6)
I believe the answer is:
shadow
'dog' is the definition.
(thesaurus)
'some breeders had owned' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'SHADOW' can be found hidden inside 'breeders had owned'.
(Other definitions for shadow that I've seen before include "Trail" , "Trace - dog" , "Dark area from which light is blocked" , "Follow closely; pale imitation" , "Image cast - dog" .)