Female animals expressed milk (4)
I believe the answer is:
ewes
'female animals' is the definition.
(female sheep)
'expressed milk' is the wordplay.
'expressed' indicates a 'sounds like' (homophone) clue.
'milk' becomes 'use' (I've seen this in other clues).
'use' is a homophone of 'EWES'.
(Other definitions for ewes that I've seen before include "Female sheep" , "Females in the flock" , "Adult sheep" , "She-sheep" , "wool producers" .)