Farmer in outbuilding pens sheep (6)
I believe the answer is:
merino
'sheep' is the definition.
(breed of sheep)
'farmer in outbuilding pens' is the wordplay.
'pens' indicates the answer is hidden within the clue (pen can mean to contain or cage).
'MERINO' can be found hidden inside 'farmer in outbuilding'.
(Other definitions for merino that I've seen before include "Fine-woolled sheep" , "The sheep provides fine wool" , "Sheep from Spain with a heavy quality fleece" , "Fine soft woolen yarn" , "Can this sheep be found in Rome?" .)