Horse half-clad? Then you must secure saddle somehow (10)
I believe the answer is:
clydesdale
'horse' is the definition.
(I know that Clydesdale is a type of draft horse)
'half-clad? then you must secure saddle somehow' is the wordplay.
'half' suggests halving the letters.
'then' means one lot of letters go next to another.
'you' becomes 'ye' (historical version of 'you').
'must secure' is an insertion indicator (inserted letters are secured by others).
'somehow' indicates an anagram.
'clad' with half the letters taken is 'cl'.
'saddle' is an anagram of 'desdal'.
'ye' placed around 'desdal' is 'ydesdale'.
'cl'+'ydesdale'='CLYDESDALE'
(Other definitions for clydesdale that I've seen before include "Powerful breed of horse" , "Breed of carthorse" , "Draught-horse" , "Heavy breed of draft horse from Scotland" .)