To raise sheep means ruin! (3)
I believe the answer is:
mar
'ruin' is the definition.
(I've seen this in another clue)
'to raise sheep' is the wordplay.
'to raise' is a reversal indicator (in a down clue, letters go up).
'sheep' becomes 'ram' (male sheep).
'ram' back-to-front is 'MAR'.
'means' is the link.
(Other definitions for mar that I've seen before include "Ram into and spoil" , "Spanish main?" , "Blight" , "Make imperfect" , "Damage; month (abbr.)" .)