Dismay Sooty's girlfriend getting up on a horse (9)
I believe the answer is:
appaloosa
'horse' is the definition.
(Appaloosa is an example)
'dismay sooty's girlfriend getting up on a' is the wordplay.
'dismay' becomes 'appal' ('appal' can be a synonym of 'dismay').
'sooty's girlfriend' becomes 'soo' (I am not sure about this - if you are sure you should believe this answer much more).
'getting up' says the letters should be written in reverse.
'on' says to put letters next to each other.
'soo' written backwards gives 'oos'.
'appal'+'oos'+'a'='APPALOOSA'
Can you help me to learn more?
(Another definition for appaloosa that I've seen is " Horse breed, with spotted rump".)