Plow pullers (4)
I believe the answer is:
oxen
'plow pullers' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for oxen that I've seen before include "Horned farm animals" , "Bulls, buffaloes, etc" , "Domestic bovines" , "Lowers" , "Domesticated bovine draft animals" .)