The possibilities are endless!!! Think about your dreams for what you want to happen with your future in horses and write about that! Or write about some things that have happened to you but in a more interesting kind of way - maybe even exagerate a little. I love writing and I have written lots of horse stories. Perhaps the best one was of a misunderstood horse called Tranquility (Quill), no one could get anything sensible out of Quill until this girl came along and figured out why Quill wouldn't cooperate... kinda long story so I wont tell it here! But write about something you love - that's always the best way.
When I bestride him, I soar, I am a hawk: he trots the air; the earth sings when he touches it; the basest horn of his hoof is more musical than the pipe of Hermes. ~William Shakespeare