Porcine pen (3)
I believe the answer is:
sty
'porcine pen' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for sty that I've seen before include "Animal pen" , "Porcine pen" , "Pigpen; swelling" , "Pigs' pen" , "Pig home or eye sore" .)