One's attached to horse (5)

I believe the answer is:
pinto
'horse' is the definition.
(pinto is a kind of horse)
'one's attached to' is the wordplay.
'one's' becomes 'pin' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'attached' says to put letters next to each other.
'pin'+'to'='PINTO'
Can you help me to learn more?
(Other definitions for pinto that I've seen before include "Piebald horse (US)" , "H [HORSE]" , "A piebald pony" , "Spotted or piebald horse" , "patchy horse" .)
