Outstanding boss for the farm (4)
I believe the answer is:
stud
This might be a double definition.
'outstanding boss' is the first definition.
'stud' can be an answer for 'boss' ('stud' can be a synonym of 'boss'). I am unsure of the 'outstanding' bit.
'the farm' is the second definition.
(stud farm is a kind of farm)
'for' acts as a link.
(Other definitions for stud that I've seen before include "Press to secure this" , "sort of stable" , "Form of poker game" , "Specified arrangement" , "associated with Press" .)