Boss in reproduction business? (4)
I believe the answer is:
stud
'boss' is the definition.
(both can mean a metal decoration)
I cannot understand how the remainder of the clue works.
(Other definitions for stud that I've seen before include "Large headed nail" , "Macho - stables - boss" , "Collar fastener - form of poker" , "Specified arrangement" , "Animal kept for breeding" .)