Boss of a horse breeding business (4)
I believe the answer is:
stud
'boss' is the definition.
(both can mean a metal decoration)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for stud that I've seen before include "Male pin-up" , "Macho - stables - boss" , "Ornamental protuberance" , "What makes shoe skidproof" , "Macho - stable - boss" .)