Avail oneself of sheep we hear (3)
I believe the answer is:
use
'avail oneself of' is the definition.
(I've seen this before)
'sheep we hear' is the wordplay.
'sheep' becomes 'ewes' (I've seen this before).
'we hear' indicates a 'sounds like' (homophone) clue.
'ewes' sounds like 'USE'.
(Other definitions for use that I've seen before include "Put to work" , "Bring into play" , "Custom - service" , "Employ - advantage" , "Habitually employ" .)