Managed to shelter old horse (4)
I believe the answer is:
roan
'horse' is the definition.
(roan is a kind of horse)
'managed to shelter old' is the wordplay.
'managed' becomes 'ran' (I've seen this before).
'to shelter' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'ran' going around 'o' is 'ROAN'.
(Other definitions for roan that I've seen before include "Of horse, with coat sprinkled with white or grey hairs" , "Horse - leather" , "Horse with a brownish coat sprinkled with grey" , "Two-colour horse" , "Bay horse with white/grey hairs in its coat" .)