Breed at the back (4)
I believe the answer is:
rear
I believe this clue is a double definition.
'breed' is the first definition.
(thesaurus)
'at the back' is the second definition.
(I've seen this before)
(Other definitions for rear that I've seen before include "Bring up - the tail" , "Of horse, rise up on hind legs" , "Back; bring up (young)" , "Rise up at the back" , "Raise - back" .)