Breeding establishment boss (4)
I believe the answer is:
stud
I believe this is a double definition.
'breeding establishment' is the first definition.
(I've seen this before)
'boss' is the second definition.
('stud' can be a synonym of 'boss')
(Other definitions for stud that I've seen before include "Lothario" , "virile fellow" , "Football boot's peg-like projection" , "Male pin-up" , "collection of cars" .)