Daughter by orchard tree spotted horse (6)
I believe the answer is:
dapple
'spotted horse' is the definition.
'daughter by orchard tree' is the wordplay.
'daughter' becomes 'd'.
'by' is a charade indicator (letters next to each other).
'orchard tree' becomes 'apple'.
'd'+'apple'='DAPPLE'
(Other definitions for dapple that I've seen before include "Patch of colour or light" , "Mottle" , "Mark(ed) with spots" , "Variegate with spots" , "Spotted" .)