Chicken breed (9)
(Other definitions for wyandotte that I've seen before include "fowl" , "chicken" , "Useful bird" .)
'chicken breed' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for leghorn that I've seen before include "Breed of domestic foul" , "port" , "Breed of chicken" , "Chicken; straw hat" .)