Grooms animal within bounds of stables (8)

'grooms' is the definition.

'animal within bounds of stables' is the wordplay.
'animal' becomes 'marten' (I've seen this before).
'within' means one lot of letters goes inside another.
'bounds of' means to remove the middle letters (the letters which form the boundaries of the word).
'stables' with its centre removed is 'ss'.
'marten' inserted into 'ss' is 'SMARTENS'.