A little cox encourages, steers and yaks (4)
I believe the answer is:
oxen
'yaks' is the definition.
(I've seen this in another clue)
'a little cox encourages steers' is the wordplay.
'a little' indicates a hidden word (a little bit of the clue).
'OXEN' is hidden within 'cox encourages steers'.
'and' is the link.
(Other definitions for oxen that I've seen before include "Horned farm animals" , "Domesticated cattle" , "Steers" , "Bovine mammals" , "Domesticated bovine draft animals" .)