Farm animal’s damage on way up (3)
I believe the answer is:
ram
'farm animal's' is the definition.
(male sheep)
'damage on way up' is the wordplay.
'damage' becomes 'mar' (to mar is to spoil or damage).
'on way up' says the letters should be written in reverse.
'mar' in reverse letter order is 'RAM'.
(Other definitions for ram that I've seen before include "needed for PC" , "Drive hard" , "Tamp" , "crowd" , "Zodiac sign; piston" .)