Horse saddle ruined in cold caustic solution (10)
I believe the answer is:
clydesdale
'horse' is the definition.
(I know that Clydesdale is a type of draft horse)
'saddle ruined in cold caustic solution' is the wordplay.
'ruined' indicates an anagram.
'in' means one lot of letters goes inside another.
'cold' becomes 'C' (eg on taps).
'caustic solution' becomes 'lye' (I've seen this in another clue).
'saddle' anagrammed gives 'desdal'.
'c'+'lye'='clye'
'desdal' going into 'clye' is 'CLYDESDALE'.
(Other definitions for clydesdale that I've seen before include "Powerful breed of horse" , "Draught-horse" , "Heavy breed of draft horse from Scotland" , "Breed of carthorse" .)