Equine badger! (3)
I believe the answer is:
nag
This clue is a double definition.
'equine' is the first definition.
(I know that nag is a type of Equus caballus)
'badger' is the second definition.
(both can mean to annoy or complain at)
(Other definitions for nag that I've seen before include "The horse to annoy continually" , "Annoy constantly" , "to get on one's back" , "Complain to or badger incessantly" , "Hack" .)