Be concerned about badger slaughter (7)
I believe the answer is:
carnage
'slaughter' is the definition.
('carnage' can be a synonym of 'slaughter')
'be concerned about badger' is the wordplay.
'be concerned' becomes 'care' (I've seen this before).
'about' means one lot of letters goes inside another.
'badger' becomes 'nag' (I've seen this before).
'care' placed around 'nag' is 'CARNAGE'.
(Other definitions for carnage that I've seen before include "Bloodbath" , "destruction" , "Mayhem" , "Indiscriminate slaughter" , "Killing of large numbers" .)