Raise, or rear, young animal (4,2)
I believe the answer is:
bump up
'raise' is the definition.
(I know that bump up is a more specific form of raise)
'rear young animal' is the wordplay.
'rear' becomes 'bum' (synonyms).
'young animal' becomes 'pup' (I've seen this before).
'bum'+'pup'='BUMP UP'
'or' acts as a link.
(Other definitions for bump up that I've seen before include "hike" , "Raise (prices)" .)