Sometimes opted to return with female farm animal (5)
I believe the answer is:
sheep
'farm animal' is the definition.
(I've seen this before)
'sometimes opted to return with female' is the wordplay.
'sometimes' means one should take alternating letters (some of the letters are taken at regular intervals).
'to return' shows that the letters should be reversed in order.
'with' means one lot of letters go next to another.
'female' becomes 'she' (I've seen this before).
The alternate letters of 'opted' are 'pe'.
'pe' written backwards gives 'ep'.
'ep' after 'she' is 'SHEEP'.
(Other definitions for sheep that I've seen before include "feature of 21/23 [NATIVITY SCENE]" , "Woolly ruminants" , "One lacking initiative (but better than a goat?)" , "Ewe" , "Wool provider" .)