An animal to keep on course (5)
I believe the answer is:
steer
This clue is a double definition.
'an animal' is the first definition.
(I've seen this before)
'keep on course' is the second definition.
(I've seen this in another clue)
'to' acts as a link.
(Other definitions for steer that I've seen before include "give guidance" , "cox" , "Direct; young ox" , "bovine individual?" , "Guide; bullock" .)