Horse managed to eat nothing (4)
I believe the answer is:
roan
'horse' is the definition.
(roan is a kind of horse)
'managed to eat nothing' is the wordplay.
'managed' becomes 'ran' (I've seen this before).
'to eat' indicates putting letters inside.
'nothing' becomes 'o' (looks like zero - 0).
'ran' placed around 'o' is 'ROAN'.
(Other definitions for roan that I've seen before include "Horse - leather" , "Of horse, with coat sprinkled with white or grey hairs" , "Type of 17's coat colouring" , "Bay spotted" , "Bay horse with white/grey hairs in its coat" .)