Newly feed a stubborn animal used for work (5,2,6)
I believe the answer is:
beast of burden
'animal used for work' is the definition.
(animal made to carry things)
'newly feed a stubborn' is the wordplay.
'newly' indicates an anagram.
'feed'+'a'+'stubborn'='feedastubborn'
'feedastubborn' anagrammed gives 'BEAST OF BURDEN'.
(Other definitions for beast of burden that I've seen before include "Animal used for transporting loads" , "Pack animal" , "Load-carrying animal ..." , "donkey, say" , "Animal used for heavy work" .)